The Ambassador class was used in the TNG eras too. (Wolf 559 and the klingon border blockade spring to mind) So that makes the Ambassador a good platform too
I wasn't disagreeing with you. Merely pointing out that the ship being a "newer" design doesn't really effect anything.
From a technological standpoint, as long as there is space and support for new equipment and the structural components can handle the strain there is nothing stopping a car/ship/plane/etc. from being in service for 100+ years. We're actually coming close to that with even 20th Century materials and construction. The B-52 bomber is slated to be in service till 2040-ish, which will be 85 years. The Nimitz Class carriers will be in service beyond 2025, putting them at 50+ years.
The point I'm trying to make with all this is that we should really look at the Ambassador from a size and capability standpoint rather than age of design. Ambassador is smaller and less capable than the Captain-level Galaxy, so in my mind it would be a nice fit at Commander level. Also, since many people seem to be put off by the current 4 nacelle cruiser designs I believe it would serve as a nice replacement.