Is it time for a new bike?

[7rider]

It's always time for a new bike. At least in theory.
You've got to ask yourself a few questions.
Start out with "what is deficient with my current bike?"
If nothing, then consider it a few bills saved.
If the triple is an issue - your Reno can be fitted with a double pretty easily, for considerably less $ than a new bike.
Are you happy enough with the Reno - fit, performance - that it is more worth it to upgrade the components vs. upgrade the bike?
That said...105 is, I've heard, a great improvement over the Tiagra stuff on your Reno (assuming that's how your bike is spec'd per the Lemond website). Shifting will be more precise and smoother.
The aluminum vs. carbon frame is a personal preference. I'd suggest you go take the 2.3 out for a fairly substantial ride and see how you like it. The Madone series this year from Trek is very nice. I"m not a big fan of carbon bikes, but I have to say, that one was probably the nicest I've ridden.
You're right..."sexy" isn't really enough of an added value!
Have fun looking....that's often the best part!
p.s. 170 really isn't that much of a burden for a carbon bike. Talk to Fred about it, but I've seen guys bigger than 170 on carbon bikes.