I stay with the same calibers in the same style / if that makes any sense - but not just one caliber:
Double action semi-autos:
I stay with 9mm and .40S&W ( and only Sig) - but I have 4 guns / 226 and 239 models. I prefer all stainless. If I carry one its a .40S&W caliber.
In 1911's ( semi-autos of course):
I stay with 9mm, .40S&W and .45acp - (my primary guns are Wilson Combat) - but I have a few others Les Baer, Ed Brown and Kimber in 11 guns overall. I primarily own 5" guns / but a couple 4" as well. I enjoy all 3 calibers in the 1911's / 9mm for range practice / .40 or .45acp for carry.
In Revolvers
I stay with S&W - and primarily in .357 mag and .44 mag ( K, L and N frames) - although I do have one older J frame .38spl / different barrel lengths, different models 19's, 27's, 28's, 29's, 66's - and then the newer 686's, 629's. I like 3", 4", 6" and 8 3/8" barrels - and a variety of finishes from stainless, Nickel and blued. So I have a little of everything in the mix / and about 15 guns.
I reload 9mm, .40S&W, .45acp, .44 mag, .38 spl and .357 mag ( I shoot very little .38 spl ) - keep them around for the grandkids.