Do you have guns that you wouldn't buy if you go back? If you knew then what you know now?
For me, I wouldn't buy my LMT MRP and HK USP Compact. Both are excellent guns, but either I just prefer other guns or they were what I thought I wanted at the time, but not really anymore.
For the HK USP Compact, it's a 40 and one of the main reasons I don't shoot that gun much anymore is cost of ammo. That and there are other guns in my safe that I prefer shooting. That was the first gun I ever bought and I don't think I'd sell it. But it's one of the last guns in my safe for consideration for taking to the range.
For the LMT, it's a VERY solid gun, been 100% reliable and a good shooter. However, being a solid and well built gun, it's also pretty heavy. So while I still shoot it every so often, my preference is my Colt and BCM that are WAY lighter. I don't regret buying it as it is a really good gun, but if I could go back in time, I wouldn't buy that same gun.