Schnert, not sure about B) and D); however, in response to A), I can only assume cost (and corner) cutting on the "el cheapo" trap door. Question C) gets a "yes" and "no": they still chrome plate the chamber, but they no longer chrome plate the bore (to the best of my knowledge). And in response to E), No, I would not buy Colt's current product line. I am, however, a HUGE Colt fan. I own seven pre-ban Colt's rifles (two SP1's, one SP1 carbine, one Sporter II, one SPII carbine, one carbine in 7.62x39, and one M4gery), and cannot say enough about the quality, performance, and craftsmanship. IMHO, I wouldn't buy a post-ban as an investment vehicle, although Colt's do hold (and sometimes increase) their value, post-bans are for shooting. I would go with a Bushmaster or a Rock River Arms if you're looking at a post-ban. For investment purposes, Colt pre-bans can't be beat in the AR15 arena....my .02 cents. Good luck with whatever you decide to do.
Cloak-