I have been wondering all week what G.A.S. meant, and ran across it on the Path Less Pedalled Sam thread - gear acquisition syndrome. I first came across the idea in Mr Money Mustache’s blog where he calls it the Purchase Justification Machine. I have 5 Rivendells now, and I am trying to quell the urge to replace sizes on two of them - my 2015 46cm Appaloosa and 2019 45cm Clem, both 26” whees, where technically the next size up would be a better fit and would open up 27.5 mountain bike tire sizes, but I am happy with the setups I have on them now. My other three are 47cm 2020 Roadini with Noodles, 50cm Roadini with Albastache and a 2019 55cm Cheviot with Albatross bars.
I didn’t notice until recently that the 2023 45cm Clem L is now a 27.5/650b wheel size, so there’s that. On the other hand, my Appaloosa is one of 2 bikes I own that can squeeze inside my Scion xB if I don’t have the Saris trunk mount rack on the car, the other being the small Roadini, and my current Clem fits the local bus racks, which the next size up probably wouldn’t. Most of my riding is multi modal commuting so I need to keep that in mind too.