Hi Don04,
I myself was faced with this exact dillema this past winter. I really liked the ideas/differences behind the Roubaix vs. the Allez, but in the end I decided that the extra cashola would be better served in getting good padded shorts, bike shirts, shoes, pedals helmet etc.
Now I'm riding my Allez Elite about 50 miles a week and I just LOVE it's handling. It can feel a little chittery over bad pavement... but I hardly ever think about that post ride... but I DO remember zipping along the lakes and passing others in my groups as I can accelerate on the uphills (and as a clyde, down of course) while the others punish themselves.
I'm weighing 275lb right now (5'11"). My LBS told me the same thing, not to worry about the carbon parts at all, that they would support me without the thought of any problems.
PLUS, to be honest the Allez just looks SWEET! The other day I had the bike in the shop and a gentleman shopping for his first bike saw mine and said Wow, that bike looks Awesome!... of course it was the previous years model (all red) and considerably different from the 2007s.
Overall, I'd just say, I was nervous about the decision too, and I've had many, many times when I've been thankful I chose the Allez. Oh yeah and the Triple ring too!!! Very handy on the big hills... don't be macho, get the triple, you'll be glad you did.