I'm not sure on the valuation of the lot- the computers themselves have an "average" eBay price of about $200 each, so the real value is in all of the accessories and software, which I don't really know how to put a price on either way.
The whole Tandy CoCo ecosystem is somewhat outside my field of expertise, as the only machines I've used have been the CoCo 1 we have with the bad cartridge port, and the MC-10. I haven't brought either to any of our more recent shows as I don't have any easy means to set them up with games or software for people to try out yet.
On the number scale you've suggested, I'd rank that in the 3 to 4 range. Technically we do have a CoCo 1, and I do plan on eventually getting that port replaced so we can use it in shows at some point. If we had access to a CoCo 3 with joysticks and whatnot, we'd most certainly put them to good use, though I don't know that we'd need a mortgage payment's worth of stuff to make that possible.