Think that's a bit harsh Lannis, although I do take your point! There are loads of non-mint workaday and not-recently-used bikes out there in the market which 'suffer' (it's not actually a disease) from non-matching numbers and a mix of bits, but they often offer a great route to affordable riding. They've almost all been mistreated at some point by owners of varying skill, and may often not run well or at all - so yes, the next guy has to know one end of a spanner from the other. But they still have a value, and the mistreatment point is just as true of shiny pricey bikes of all and any marque, which I have found are often worse!
For a very good handle on value of the bits, look at AMC Classic Spares web site and 2nd hand parts list, and subtract whatever for the fact that it's a private sale. They have pretty much all parts for all twins 2nd hand.