The upgrades from say, an XL to XL Diamond, requires a new PCB and new CD (although the Diamond might be a hard drive model, I'd have to check again). Check out Merit's site to see the upgrade chart
www.meritind.com. I should also point out that I'm not 100% sure that just any touchscreen will work with the PCB. I'm trying to find that out right now, because some of the touchscreens on Ebay go for around $80. I talked to a distributor of these and he mentioned that all of the ones he sells have a name like Microtouch, he couldn't remember off the top of his head. Happs sells a touchscreen from both ELO and WellsGardner that they state are for Merit machines
http://www.happcontrols.com/monitors/49091900.htm, so I'd look into that too.
I'm not bidding on these right now, but even if I was, the highest bidder always wins, so go ahead and snipe them if you want.
Anymore questions or ideas, let me know and keep this thread going. I'm not any kind of expert, but perhaps one will come in here to help out, if needed.
Troy