Yes, again this is the kind of stuff I might not have considered, so thanks for making me think about it...
Currently I own 1 set of wheels (the ones that came with the bike) and 2 sets of tyres. So I have indoor tyres and outdoor tyres (clinchers), which I'm swapping twice a week, outdoor mid week, indoor weekends. Main reason for the purchase was to get onto tubs indoors, and having at least indoor/outdoor wheels will instantly save me that constant tyre swapping hassle. (Yes I could have bought indoor training wheels for 10th the price of these, but the opportunity arose to get these and it might never come again, so I took the plunge).
About hub threads/gear changes, I haven't yet needed to change the sprocket at all for the different training sessions, accreditation programs & mock races we've been doing, 15T seems to be doing the job nicely. But admittedly exposire is limited as I've only returned to the track last autumn after a lot of years away (during which time all the old gear I had got sold/given away). Anyway, I've a couple of chainring options between 48 and 51 that seem to cover most/all needs so far.
If/when I get more picky about gears, become stronger, race more and start to appreciate the different requirements for different events/sessions (and different tracks), by then I'll probably have 2 or 3 more sets of wheels for exactly the reasons you say. But for now sticking to that 15T and swapping chainrings if necessary will do, so the hubs should be safe.
Comfort I really had not considered. If I can ride for 4-6hrs on a stiff road bike with carbon rims and bonded carbon spokes (Lightweights) and be ok(ish) by the end, how much worse can a couple of hours indoor track riding be on these super stiff Mavics? Guess I'll find out!
Thanks for the debate(s), hope I'm not sounding like a t**t.