Actually, in browsing this board as well as the "old" one, I've seen quite a few pics of active duty military types who have chosen to fit fixed A1 or A2 stocks on their M4's. Most of the photos have been claimed to have been taken of Rangers, SEALS, and other SpecOps who are allowed a degree of latitude in personalizing their weapons. Besides the fixed stocks, they also had a nice complement of lights and optics hanging off of them. Didn't look at all bad.
In fact, I can imagine missions or operator specs that would make this a reasonable decision. For instance, my 6'2" friends think my Colt M4 collapsable [stock] is really short, even at its longest.
I see where you're coming from -- I'd hate to have a "collapsable look" stock that doesn't collapse. Throw an A1 stock on it. Better yet, find one of those elusive Canadian military stocks that are A1 length buy made of A2 material (has *anyone* confirmed their existence in the US aftermarket?).
If it makes you feel better about the rifle (just like some like a fixed collapsable), go ahead and do it. If I had an extra $600 laying around, I'd get in on this deal too and probably throw an A1 stock on the rifle.
No, it won't look funny. In fact, some may mistake you for a someone who knows enough about his preferences that he isn't afraid to buck the trend. [:)]
Enjoy your rifle!
EDITTED to add the word "stock".