Cycling isn't getting expensive, it's always been expensive. As for old versus new, I have a 1979 Colnago that still runs like new - actually, better than new; carbon fork, bladed wheels. Could I have bought a better bike with the money I've put into it since then? Absolutely. Bikes are like cars; the advances made in the last 20 years are more than window dressing, they're quantum. They're safer (you can shift and still keep your hands on the brakes in a paceline), lighter and, with sealed bearings, lower maintenance in the overall.
If you really want your dealer to love you, test-ride a 2005. If the difference is huge, buy it and keep the others for beaters. If it's not, keep maintaining the old ones at your current level. You're out an average $1,000 a year, regardless.