If you like the AC series, then I don't know why you wouldn't have picked up Revelations already. If you're not that into it, then maybe refrain. As for inFAMOUS 2, yes, yes, and yes. I'm a stickler for playing my games in order, so I'd recommend playing the first one, well, first, to get the most out of the second one.
If I hadn't already played them both, I wouldn't hesitate. $20 for these two titles is a fantastic deal.
@Zenogiasu: I didn't pick it up 'cause I never had the money. I love the AC series. The only reason I hadn't bought these games yet was because I didn't have the money. And yes, I like playing games in order as well, it's the only way I'll play a game. That's why I'm not getting Witcher 2 on 360.