Your problems are "running out of room" and getting "the look". Having too many mowers should not be considered a problem IMO, and in your case they all sound like good ones.
I suggest you take a look at MaxWestern's post on constructing shelves so you can fit more mowers into your existing shed space.
Recently a mate needed a mower. After careful consideration he drove off with a Victa Quantum 60 in excellent condition and I was down to just 18 mowers (runners that is). The next weekend another mate turned up with an old unwanted Rover which is now a good runner.
Culling doesn't work it seems.
