My Mark III sounds almost just like a IIC+ with the right tubes in it.
I'm gonna sell it for $2500. Sound about right?
If not, I'm not buying into mojo, the amp -is- mojo.
I think you should pay for what the amp is; condition, options, hi-fi tubes, recent repairs, etc. Paying for "history, belated awesomeness, can't live without factor, etc" is chumpy.
Otherwise my Orange Tiny Terror would be worth about $1500 (in ebay money of course!) too. That sucker is pretty bad to the bone for a 15 watt. It actually holds its own against my Mesa, i'm not going to lie.