Dunno about cars, but I have 3 bikes;
Workhorse/Commuter - 1992 CBR 600F, streetifightered, looks battered and not worth nicking. I am happy to park this up in bike bays in London, and don't mind racking up miles on it as it's not that expensive to service.
450 Supermoto, shortly getting off road wheels for it so I can use it green laning as well, purely for fun on the weekends, off road and on track
1000cc V-Twin sports - This is purely for fun, weekend rides, as well as track days.
Cost wise the workhorse is the cheapest to service, 2nd most expensive in petrol, not particularly exciting.
The VTR is the thirstiest for petrol by far, costs more to service than the other 2, but is great fun.
The supermoto is cheapest per service, but needs servicing most regularly and is probably on par with the V-Twin, cheapest petrol wise.
I'm also thinking of adding a 4th to the stable at some point, pure track bike
Could I make do with 1? Probably
Would I trade up 3 bikes to get one which is the current in all singing and dancing model? Not a chance.
Cost wise means I stump up for tax and insurance, but not having to worry about having my nice bikes nicked or damaged more than makes up for it for me