Staying with the PS3 is a valid choice because there are still good games coming out for it but a year or two in the future will surely see AAA title dry up for the PS3 because the tech just won't be able to handle the newer games properly.
Which technically we're already seeing happen. Shadow of Mordor just came out for PS3 and 360, and there are already large enough differences such as the nemesis system, AI and animation., though granted, the latter could very well be due to bad optimization.
One reviewer who's played both the PS4 and PS3 versions has noted the differences that go beyond the superficial:
http://kotaku.com/shadow-of-mordor-is-way-less-fun-on-old-consoles-1660387779