Componentry did it for me. The more I ride in the drops, the more I'm annoyed by my Sora shifters. And, the more I try to ride hills, the more I feel that I need a wider gear spread, which would require an mtb derailleur. And I wonder if my rims contribute to the brake squeal that I just can't get rid of, so that makes me want new wheels. At that point, for the money involved, it makes sense to just upgrade to a whole new bike.

Unfortunately, I'm in your situation-- I can't justify it financially. One day, but not soon enough...