Regarding your last point, I have also some times wondered about the relationship between the amount of wear and the required service interval. I presume the standard recommendations on the service interval, typically around 5 years, are based on wearing the watch all the time. But when you have many pieces and wear a specific watch only part of the time, this should naturally lengthen the time before a service is required for that watch (all other things being equal) - at least if you don't use a winder (which will cause continuous wear and tear, although maybe not quite as much as actually wearing the watch - less shocks etc.). The question would then be, is there a reliable relationship between the amount of wear and the service interval? For sure it does not scale linearly - e.g. if wearing a watch seven days a week equates to a recommended servicing in 5 years time, wearing it only one day per week would hardly extend the service period seven-fold to 35 years. So any relationship would be sublinear, and there is likely to be some kind of limit as well - that is, a service is probably required at some point, even if a watch is not worn at all (due to the oils drying out etc.) ;-)