I would upgrade the wheels. Nicer wheels makes a huge difference, IME. Plus, if you get a new, nicer, bike later - odds are that the wheels you buy will still be nicer than what comes stock on that bike and you can switch them out. Upgrading to a carbon frame with Tiagra components just invites, later, feeling like you might want to upgrade to 105/ultegra. In the long term, independently upgrading frames/components is the most expensive way to go in the long term. However, if buzz from my aluminum frame were there and bothering me, and my only near term option for relieving that were to replace the frame with a carbon one, I'd consider that.