Since the PS4 isn't backwards compatible at launch, the PS3 would be a worthwhile budget purchase since it has a large library of games, especially at the end of its life cycle. It should cost around $250 or so
That depends how many of the current gen games have you played/ completed. If anywhere near the same amount as I did (I don't have a ps3 but I have a pc and Xbox) then no it really isn't and saving an extra 2-6 months and buying the new gen is really worth it.
On the other hand ask yourself do I really need it?
Do I like the games that are available?
Can I afford to save for next gen?
Do you have a blu-ray player? (if the answer is no then it is very much worth it indeed. Not only because you now have a blu-ray player but because you can game on it too)
There are still many publishers that cater for that market (unfortunately)
Liek Rock* with new releases like GTA V
So if you need it, don't have another gaming platform (like a medium range gaming pc) I'd say it is worth it. Unfortunately Sony said they aren't going to cut the prices of the PS3 just because the PS4 is coming out (probably getting marketing ideas from Louis Vuitton) the bastards
However if you are smart you'll check secondhand sites like Ebay because even though Sony might not give discount on old gen consoles people looking to upgrade to next gen and getting rid of their old consoles will.