Essentially all you'll ever need to do to 7400/6400 and 7700/6500 STI shifters is spray Tri-Flow lubricant the mechanicals through all the crevices (while shifting up and down!) in the lever when they get gummed/gunked up. A thrashed pair of shifters is not ever something to judge a shifter's quality/durability from. Between accidents/crashes and people just being animals to them (and then ignorantly telling everyone how they "just don't work"), it's quite the mine field of opinions to go through.
Each generation has their own shift feel, and I like all of them and think they work plenty well. The 7700 shifter body cross-section is different from 5500/6500, and IMO for the better as I like its more rounded top corners (vs. squared for the others). There is a shift mechanism plate in the 7700 lever (right/rear) that eventually wears out and makes it firstly hard to shift, then impossible to shift. Shimano should have been ok with 10 more grams and made it bulletproof for eternity instead of "just" several decades.
7400/6400 tend to be rebuildable if need be, but they're really strong and don't need it if taken care of. Sure, a Campagnolo Ergo shifter from the '90s "still works!" and "lasts forever!" and "is rebuildable!" which is great provided you can find the small parts for all those times you invariably need to rebuild them. The Shimano stuff works from Day 1 and was designed in such a way so as to not need rebuilding.
The height of the silver groupsets was the 7800/6600/5600 10-speed era. Those will always hold a special place in my heart. 7900/6700/5700 are plenty capable, and the shifting of Dura-Ace 7900 is really good. Never had a problem with them, and the front shifting is excellent. I haven't tried 9000 yet, but want another shot at 6800 as the front shifting experience with an internally-routed frameset (Cannondale CAAD10 disc) was quite labored, and I don't think that frame gave that groupset a fair shake.