I guess I have opened up a can of worms. 
My thoughts...
Collector - someone who makes an actual purchase of a machine to house in their home/shed/garage and maintains it in working order for personal (or others) enjoyment and. It may be one, it may be 1000 - the only restriction being space or disposable income for that individual. The fact that someone has actively sought out to purchase a non-mainstream product like a pinball machine to put in their home (as opposed to a bike) makes them a collector in my mind. 
if thats your interpretation of a collector, you go with it....but you're wrong ;-)
I buy a LOT of non-mainstream products, it still doesn't mean i'm a collector, i buy them coz i have a use or get entertainment from them, it's still not "collecting"
Anyhoo...
