There will always be demand for parts, especially if an item has been out of production for years. Having said that, I've been pleasantly surprised at the ease of getting new 'old stock'/repro/equivalent bits for my oldies. Due to the 'net, easier than it was in the '70's, I think.
Personally, I don't like the idea of 'breaking' for spares, unless it is beyond repair. But that's just me.
And. of course, if the gun is well worn, you may find you can offload some bits (body,grips,barrel, piston, say) & end up with a jar or 2 full of shagged out components, that are no use to anyone.
My 2p worth.
Bru
Webley Mk3 x2, Falcon & Junior rifles, HW35x2, AirSporter x2, Gold Star, Meteors x2, Diana 25. SMK B19, Webley Senior, Premier, Hurricane x 2, Tempest, Dan Wesson 8", Crosman 3576, Legends PO8. Kral Puncher K.