I did not upgrade to an "aero" bike, but I did spend many dollars (> $1400.00) upgrading the bike I have (which I purchased on sale for around $400.00), and in the process, with the new components, shaved about 3 or 4 pounds from the bike. I now enjoy the bike even more than I did before and I do not feel the need to upgrade to a new one...however, that does not mean I do not look.
I may upgrade n + 1 at some point in the future...but not until I can really afford the "dream" bike. I do not want to upgrade to "just another bike" I will only want to replace in a couple years.