Here's my opinion, and it's worth every penny you paid for it.
A light on an AR isn't necessary. Lights are fine for close-combat firearms like handguns and shotguns, but AR's aren't suitable for home defense unless you live in the middle of nowhere and you don't need to worry about overpenetration.
I'd get a good sight -- EOTech or ACOG -- and a vertical foregrip. I'd probably add a two-stage trigger if it doesn't have one already. A sling is awfully convenient, too.
Anything else is probably just tacticool which increases weight and doesn't add a heck of a lot of functionality.
Not so good: