I have mine sitting in the closet. Once you jump to PS4, it becomes obsolete aside from digital purchases (I believe they should carry over personally, but alas).
Sheer value in exsisting library, yes PS3 is better (this is the whole PS3 vs PS2 convo from a decade ago all over again). However if you have any interest in current gen titles, the PS3 will be worthless as most games coming out from 2016 onward will be current gen only, and the trend will continue to grow as time goes on. So in the end, it depends on how badly you want to play new games now that last gen is finally being put to rest by most devs.