I'd say that the use of the car crash of a metaphor is highly plausible, and would probably make the song more credible, but I'm gonna take it at face value for my interpretation.
Firstly, I think the guy (I don't think that Paul is writing as himself - hence the use of a puppet in the vid and not a trace of the 'pol anywhere) lost his partner in a fatal car crash. I think perhaps she didn't die instantly but that she ended up in hospital and didn't make it. The song is about the guys struggle to come to terms with the loss of his partner (who I think may have been dead for some time now) in the face of feeling romantically towards somebody new - Sandy.
Right, now let's back all that up:
"Rosemary, Heaven restores you in life" - Let's everyone know she's dead right at the beginning, also shows us he believes in Heaven and believes that she may still be aware of everything that's going on. This is backed up the next few lines:
"You're coming with me, through the aging, the fear and the strife" - This line could also be a reference to the wedding vows:
"I offer you my solemn vow to be your faithful partner in sickness and in health, in good times and in bad, and in joy as well as in sorrow. I promise to love you unconditionally, to support you in your goals, to honor and respect you, to laugh with you and cry with you, and to cherish you for as long as we both shall live." I only just thought about this one, but everything he says 'aging', 'fear', 'strife' it's all negative stuff, and in the wedding vows you promise to stick by each other even in times of trouble so maybe they were married and he's saying that even though she's no longer here, she's still going to be with him through all the things they promised when they got married.
"It's the smiling on the package, it's the faces in the sand, it's the thoughts that hold me upwards embracing me with two hands" - Again, I concur with what others have said - he feels her around him (the embrace - most common meaning is a huge between lovers e.g. a lovers' embrace) and sees her everywhere (sand, packaging).
Now for the next lyric I've found two different interpretations of the actual words he says. I thought it was "Right will take you places" but I've read elsewhere people think it's "Write, we'll take you places". It's almost impossible to decipher by listening so I'll interpret both.
"Right will take you places" - She lived a good life so she went to Heaven.
"Write, we'll take you places" - Stay in contact even though I'm falling for someone new, you won't be forgotten, you'll always be there with us too. This line goes better with the next one "Yeah, maybe to the beach"
"When your friends they do come crying" - Again, suggests that the person has died as her friends are also affected, it's not just the guy singing the song that has lost her.
"Tell them now your pleasure's set up on slow release" - she's going to be happy for a very long time, i.e. It will take a long time for her pleasure to diffuse because it's on a slow release. Also as he says "tell them" it suggests he's saying let them know you're happy it might help them come to terms with things.
"Hey wait, great smile, sensitive to faith not denial." - Maybe she was always a happy person, even when she was in hospital facing the likelihood she may not pull through (not denial - she wasn't in denial about how serious it was), sesitive to faith, perhaps she was believing her faith might pull her through.
"But hey, who's on trial?" - He reflects that he's just been judging her behaviour after the accident (noticing that she faced up to things and put on a brave face), but realises that it wasn't her fault, she was the innocent and she died. "But hey, who's on trial?" as in "Why am I judging your behaviour after that horrific accident, you had every right to behave however you pleased." Alternatively, after thinking about the next line, it could be that he was driving and feels responsible...
"I've spent a lifespan with no cellmate" - He's the guilty party (feels responsible) as far as he's concerned (maybe not in the eyes of the law, i.e. maybe another car hit them but he was the driver) referenced by the "cell" - prison - and he's also managed to go this far without felling anything for anyone else "mate".
"The long way back" - Could have several meanings. Perhaps that fateful night they took the long way back? Perhaps they didn't and he wishes they had? Perhaps he just means it happened a long time ago?
"Sandy, why can't we look the other way?" - Why am I having these feelings for you, when I still love and miss Rosemary?
"we speaks about travel
Yeah, we think about the land
We smart like all peoples
Feeling real tanned" - sounds like he's imitating ghetto speak. Angry at black people? Maybe it was a group of black people who were driving the other car?
"I could take you places -
Do you need a new man?
Wipe the pollen from the faces
Make revision to a dream while you wait in the van" - He starts thinking about Sandy again, and quick as a flash Rosemary comes back to the forefront of his mind:
"Hey wait, great smile, sensitive to faith not denial"
And then again, he wishes he didn't feel this way towards Sandy:
"It took a life spent with no cellmate
To find the long way back
Sandy, why can't we look the other way?"
"You're weightless, you are exotic
You need something for which to care" - This could be about Rosemary and/or Sandy. With Rosemary "You're weightless, you are exotic" - She's weightless because she's no longer a physical presence and she's exotic because she's different to everyone else. With regards tos Sandy, it could be she's extremely thin (not as goos an interpretation as with Rosemary I feel) and she's exotic - maybe she's foreign, maybe she's black and that's why he was mimicking ghetto talk earlier in the song. Maybe "you're weightless" is a reference to Rosemary and "you are exotic" is a reference to Sandy. The "you need something for which to care" could be a reference to either as well.
Then back to why is he thinking about Sandy, why can't he just forget her?:
Sandy, why can't we look the other way?"
Then he seems to start asking for to remember Rosemary and keep her with him so he doesn't feeling the wanting for Sandy:
"Leave some shards under the belly
Lay some grease inside my hand
It's a sentimental jury
And the makings of a good plan" - I think this is metaphorical, I don't think he really wants glass in his belly or grease in his hand, he just wants a permanent and prominent reminder of Rosemary so he doesn't move on.
"You've come to love me lightly" - He can feel her presence
"Yeah you've come to hold me tight" - He won't let himself move on, he allows her to hold on him still.
"Is this motion everlasting
Or do shudders pass in the night?" - Will he always feel like this, or does he just need more time to come to terms with it? Alternatively, maybe he wonders how long until he forgets about Rosemary altogether because he doesn't want to?
"Rosemary
Oh, Heaven restores you in life
I spent a lifespan with no cellmate
The long way back
Sandy, why can't we look the other way?" - I've explained this enough.
"You're weightless, semi-erotic,
You need someone to take you there
Sandy, why can't we look the other way?
Why can't we just play the other game?
Why can't we just look the other way?" - Sounds like this is all about Sandy so the other references "you're weightless, you are exotic" probably is as well. I feel here he is practically begging and pleading to forget about Sandy because he feels to consumed with guilt about what happened to Rosemary and also about letting her go.
