everyone missed the obvious answer: every man needs at least 2 AR-15's, so here's your excuse to get another one.
plus even if you put your red dot sight back exactly where you took it off, and ditto for the scope you want to get, always a chance it gets off alignment a little. it's one thing to miss some targets at a 3gun tournament, another to miss the bad guy (or hit the hostage) while on duty.
i too am curious on the colt, just read about it. review said they guarantee 1 moa and the test rifle averaged something like .8 or so.