I don't race, so can't give you advice in that direction. However, I have spent many, many thousands of miles on road bikes, both for fun and commuting. The advice you've gotten from everyone else, so far, is spot on.

Components are important, yes, and they do make a difference, but not equally from the standpoint of performance. Some make more of a difference than others.

When shopping for a bike, I start with the frame. You can always upgrade bolt on components like shifters, derailleurs and so on, but the highest end components can't turn a lower or mid level frame into a top end frame. I'd rather have a better frame with lower end components than the cheaper frame with higher end components. The frame is really the heart of the bicycle.

Next I look at the wheels and hubs. Derailleurs and shifters get most of the attention from folks shopping for road bikes, but actually, one of the most important components on a road bike, in my experience with upgrading, are the wheel sets. Huge difference in performance between an entry level set of rims and hubs and the good stuff. Would rather get a new bike with top end wheels and save money on the derailleurs and shifters, but new bikes aren't sold that way. Upper level wheel sets aren't found on entry or even a lot of mid level bikes.

Then, I look at the shifters and derailleurs. Have only used Shimano on my road bikes (but love SRAM on my MTBs). My minimum on shifters and derailleurs has always been 105 and for good reason. I've probably have north of 20K miles on 105 and have never had a single failure. The new Tiagra, though, is actually pretty darn good, very comparable to what 105 was in the old days. I love Ultegra, though. It really is smoother and quicker. You'll never regret going Ultegra.

Brakes? Well, I still like traditional caliper brakes on road bikes, but you just can't beat the practicality and performance of disc brakes for a multi use, all weather bike. Quicker and easier to change wheel sets, too.