I dont' see the value in it yet either, but maybe the offers will improve. Right now the big thing is that you can only initiate cross-game chat if you're a + member, but honestly, most people i've run into on PSN don't voice chat anyway because unlike the 360, there's no packed in microphone that comes with nearly every console.
sucks that you don't get the permanently keep the games either.
i've heard that PSN+ is gamesharable though, so instead of $50, it could be split to be $10 / person, which makes it much more reasonable. Check Cheapassgamer for details.