I think it's really, really hard for artists (which is the perfect word) to pull this off (be as good now as they were in the 60's). Their lives are entirely different, everything has changed and it's hard to have that 'hunger' that made them so successful when they started out.
Carl Wilson is a great example, for years we kind of held him up as the artistically pure one, everything he did in the 60's and 70's was pretty respectable, then in the 80's he's doing songs for the Problem Child soundtrack.
Well, he had kids! he was middle aged. He was rich. Everything changed... so to him, it was probably a good idea. As fans we're all going "what the f***
".
Dylan is the most interesting to me, because in my opinion, he's the anti-, anti-establishment guy. People claim he sold out but he never was about that to begin with, he was PRESENTED as a rebel but in my opinion didn't seem to care how he was seen or didn't want to have to play up to that rebel stereotype. It puts him in a unique position, where more than most other artists his music in my ears can still come off as very pure to him even when it's largely commercial or completely different than something he's done before. The stereotypes he's not living up to with some of his music he never presented in the first place. Hard to explain; I guess my point is a lot of artists come off as hypocritical when they change their style but Dylan doesn't.
Paul is an interesting example too, because in my opinion he's the most talented singer songwriter alive and has been since he turned 20. It's hard for me to be critical at all of his new music because when you're on the level he's on (greatest living musical legend) it's almost like we're peons and should be happy for anything he gives us! He also has ENORMOUS street cred in my opinion because of what he did with Wings in the 70's; spent a decade making music that a lot of people would consider throw away, but was still just as entertaining and talented as his pop masterpieces with the Beatles. So yeah, something like Jenny Wren I listen to in awe and think this is how it must have been to experience Picasso or Da Vinci while they were still alive.
Another interesting this is, the guys in the 60's changed music because their style was so solid. So Dylan for instance of course borrowed everything, but there was nobody quite like him, before him. He blew everybody away in the 60's... he can't do that again, with his style and talent because there's somebody like him, before him, now... himself 50 years ago. No new ground to expand into...
Same thing with Paul, a lot of the love he gets, to be honest, is because in America we weren't familiar with British pop stars, and especially ones that talented. So everything from the Beatles energy in their music, to the way they borrowed their English'd-up american R&B and put it into their sound, to even the way they talked, dressed, and behaved was so foreign to American audiences at the time, it just Blew. Us. Away! Nobody, even Paul himself can live up to that because we've seen the British pop thing done very well by tons of different people ever since.
So it's pretty hard to judge any 60's act vs. their current stuff because the music scene is so different.... however, when it gets right down to it, brass tacks and all, most of those guys (and gals) made it big because they were talented, and most of them are still every bit as talented as they ever were... it just doesn't stand out in as stark of contrast because the way the world's changed around them.
Can McCartney, Dylan, etc. still write a good song? Hell yeah... but will it be as groundbreaking as that same song presented to a 1965 audience? Doubtful.