Yeah, I forgot about the no-upgrade thing! I guess if you play with a high tech start, that wouldn't matter as much, but I don't. Research is a big part of the fun!
Come to think of it, even if you do start with all the tech, I'd think you'd still be altering your designs for maximum effectiveness against whatever your enemy is using. I know that my ships go through numerous tweaks and Versions (adding or subtracting PD, shield-piercing weapons, and so forth) to try and counter what the enemy is packing.
There was a message (somewhere around here) saying MM is considering ways to refit units but that it is low on the list because of the amount of reworking that would be needed to add the feature. Or at least I think that's what it said.