Re:
Thanks for proposing this topic. This is something that bothers me lately as I'm taking a minimalist approach to everything in life, bikes included.
I'm on a slow but gratifying path to reduce my number of bikes. Not sure if I'll ever reach the "one only", but for sure it feels already better to have less. Once in another forum a guy had as profile signature "Each bicycle owned exponentially increases the probability that none is working correctly", and that was too true for me to forget.
At a certain point I was above 10 bikes, but I am currently on 7, with one currently on sale and another one on the bikestand getting the final fixes before putting it on sale too. Another one will be taken to my parent's place, so I have a bike when I visit.
From the 4 remaining, one was given to me, a 40 year-old folding bike from the in-laws which I only use once a month when we visit them, because folding bikes are free on the train. Otherwise I would happily give it away anytime, it's heavy as hell and uncomfortable after 5 km.
I use my bike not only as a leisure tool but also as main means of transport, so I would need at least 2 bikes so if one breaks down (or just have a puncture and I don't have the time to fix for next day) I have a replacement. So on my paring down I think I will stop at 3:
-my touring bike, which is also my daily transport
-a relatively new mtb, which is purely for leisure/weekend rides
-my first mtb, which acts as back-up for the previous two, plus it has huge sentimental value
Whenever I get to just these 3, hopefully by next summer, I will pause for a while and then re-think. I believe I could just do with one, the old mtb that can perform decently as commuter, tourer, or mtb with minor tweaks, so I might go for that as next step. I can always take the train whenever the bike breaks.
For everybody else, I know we say "what is wrong with my X bikes?" or "why not if I can afford it?, etc. It's all fine and good, I'm only saying it's also good, from time to time, to self-question (not only on bikes, also on t-shirts or beer glasses) how much is enough and where the fun stops.
For me, these questions helped:
-Do I start to have storage problems? Problems to find a place for all the bikes, or to find a certain piece, or to get a bike at the back of the pile... Or even friends come to visit with their bikes and I have no place to park them.
-Am I starting to get economic problems because of it? To pay for all the bikes, the gear, the maintenance,...
-Am I starting to have issues to keep all bikes in top mechanical condition? That was the deal killer for me, I noticed more and more bikes were falling into the backlog, and sometimes doing mechanics was becoming more of a chore than fun
-Am I getting into discussions with my partner about the bikes? Of course, this also depends on the partner, some are quite ok with 20 bikes in the garage and others start shouting after the second bike...
-Do I have bikes that have remained for a long time unused? Do I have a lot of "projects" unfinished?
-Do I waste time looking online for "deals" or parts rather than doing productive stuff, or just riding?
-If I ever have to move, would my bike hobby become a burden?
I'm also paring down my "spares/parts bin", plenty of things there I know I'll never use that I either sell or donate to the local university bike workshop.