Yes, sure, n+1 applies to power tools just as much as to anything else.
I still reckon that, given a couple of hundred to spend on drills, I'd go for a decent cordless like the Mak or the Hitachi mentioned upthread, and a reasonably lightweight SDS. I don't think an SDS is overkill for domestic use if you do a reasonable amount of DIY - but then I have just sunk 8 electrical back boxes. Soft London brick - faced with bastard hard render.
Something like the DeWalt flipper drill sets -
http://www.amazon.com/gp/aw/d/B000051WR8 - can be really handy in reducing faff for pilot holes, countersinks and driving, as can quickchange bits, though they tend to wander a little.
If I still felt the need for an extra power driver, I'd probably go for one of the lightweight screw/impact drivers that are around. (Extra cordlesses do me fine at the moment ...)
DeWalt Extremes - yes, they're good, but I do prefer the Bosch.
(Paddle mixer drills, Kangos, that sort of thing - the hire shop keeps them until and unless I need one for months ...)