First, only YOU can decide whether the price of bike X is worth it to YOU. Second, if you want a road bike, get a road bike. If the clunker (or a car or bus) is more appropriate for your commute sometimes, then use those other options when you need to. Your want of a road bike seems to go well beyond your commute, and although cross bikes are nice, sometimes it is hard to make them into speedy road machines much more than your MTB with slicks due to cross gearing and wheels. (Some wheels could take skinny tires but if you want thick tires for commuting, then that is a pain or at least requires 2 wheelsets if you want to go with skinny ones for going fast). Plus, decent cross bikes really aren't going to cost any less than the road bikes you're looking at.


As for what componentry you want/need, here are my thoughts: Carbon seat stays are not necessary..and possibly not the fork. Some manufacturers of aluminum/carbon mixed bikes go with the theory that carbon is more important in the front triangle and fork. So you'll find a stiff front end that molds into full aluminum towards the rear. Others put more carbon in the rear triangle. Sometimes this is in the seatstays. Sometimes the chainstays. Sometimes both.

In any event, low level carbon isn't going to give you much noticeable improvement over full aluminum or alum/carbon mixes. All are fine for a first bike. Ride them all and see which bike gives you the ride you like the best. This may have a lot more to do with geometry and the grouppo than the frame material at this price point.

Personally, I wouldn't get anything below 105, because Tiagra and Sora are a pain in my butt to keep tuned properly, and they just aren't responsive. It would make me not want to ride the bike. Now for serious racing, I prefer Dura Ace performance, because well, having built up a DA bike, it is so hard for me to go back to 105/ultegra on my other bike, even though it works just fine. In fact, I may snap up some $200 closeout 7800 model shifters for that bike to help me get on it more often this fall, because it's good for long training miles... but I digress. Is 105 or better necessary? No. Would you outgrow Tiagra? Maybe. It's hard to tell. But the good thing is that if you stick with 9spd, it will be cheaper than the equivalent level for 10spd.

By the way, if your university has a cycling team, collegiate cycling is a great way to give racing a try! It's typically more low-key (more intro categories), and it's cheaper than jumping into your local amateur scene. NCAA eligibility rules don't apply, so many of the racers are grad students.