I think I'm like you – started with a basic commuter, then a basic mtb when I got the bug
since then I have replaced the basic starter bikes – and now have 5 bikes
However they all do a different job (ss commuter, "proper" road bike, hardtail, single speed MTB, full suss MTB)
I am happy with all my bikes and have no plans to change any of them (bar upgrades to the odd individual component here and there)
I do think about new bikes – buts its always a different type of bike than I have currently (track bike, cross bike, tourer, cargo bike blah blah blah)- I don't think I could get that excited about buying another single speed say, the one I have does the job just fine