I don't agree with being able to ++ someone separately from something they've written (for reasons I'll explain), but I ++'d you, as it's an interesting idea, and displays unselfish gratitude on your part.

The XP is certainly fun, but the true payoff is feeling like you've helped someone out.

When I get a private message from someone I've never met in person, telling me that my input was valuable to them, it really makes my day!  Similarly, when someone responds with a follow-up post thanking me for helping, it's a nice affirmation of my participation in the learning process, and gives me the added benefit of being "praised out loud" (like when a teacher compliments your answer in front of the class).

Once you've been here a bit longer, I'm betting you'll see that this is where the real reward is!