My Madone 4.5 came with Ultegra RD/FD and shifters and 105 brakes, cassette and chain. Via Trek Care+ my chain and cassette have been upgraded to Ultegra and I can notice a little bit better shifting (of course it could also be my imagination). Is it worth the $400? Probably not unless the bike rides that much better. For what you're talking about doing 105 is more than enough.

Enjoy the ride!