Thanks for the replies everyone. Some great thoughts here. I'm mulling over...
- Original versus licensed theme. I can see that a more popular theme will naturally have a larger audience and therefore, in theory, command a higher price, but then some of the most popular machines are original themes (MM, MB (kinda),
AFM etc) so a machine that is recognized as being great to a core audience can equally command a high resale than a machine that has wide appeal to a more mainstream audience.
- Perhaps the same as above for low production vs high. Low production certainly increases rarity, but it might also imply that it's not a popular theme, or one that's well liked by the core audience. TAF still sells well, so the sweet spot is low production, but a machine that is considered great (struggling to think of a good example here -
BBB? TBL (despite not being 100%)).
- Great point about the move to TV displays. I could see that in a few years, as people get used to a bigger display, a machine with a standard DMD would suffer more in depreciation in the same way that alpha numerics to DMD did (although this might be an over simplification - I wasn't into alphanumeric machines, but DMD era also brought in more complex s/w, modes etc)
- Regardless of price, I still need to love the game. I've not owned a JJP machine before but I do like a fair amount of toys on my playfield and it seems that JJP are upping the ante here. Could be wrong, but Stern seem to be more cost conscious and therefore more sparing on playfield hardware.
- Software could rejuvenate a machine that's struggling. GB might be a good example - if Dwight sorts himself out and gets the update out it might give the resell value a bump.
- The classics are still the best bet as they've had as much of the NIB deprecation they're going to get, however if CGC remake everything even the originals still lose value.
- Figuring the point at which a machine is no longer depreciating, but is either holding it price or starting to appreciate (more than inflation) is going to be hard given all of the above. Maybe I need to spread bet and double my collection

Maybe there's a formula somewhere in here. Might be a job for AI
Thanks again
John