I don't know if I'd put an abnormally high value on it -- but I have been known to pay more than "fair market value" for certain music items...including Sunn.
There are a lot of things about the old Sunn company gear/company that I appreciate. A lot of these traits don't mean squat to other people. I had a respected amp tech tell me that Sunn was garbage...that paying more than $50 for a 200S-like Sunn (2x6550/EL34) amp in excellent condition was a rip-off. I couldn't understand that. How can one tube amp with relatively similar construction be worth so much and Sunn be "crap"? It's not like comparing Fender or Marshall and Sunn is like comparing apples and Hyundais. Hmm...nevertheless, those types of amps in various states of repair regularly go for over $200 on ebay. Somebody must want them...or have the money to buy them.
If I like the amp, then I will pay what I think it's worth. Personally, I like the sound of the amps, the construction, the Sundholm story, the PNW origins of the company, the looks, etc. To those like my amp tech who hate Sunn tone -- not to start a "religious" argument here but I am pretty convinced that playing technique and skill (in one's fingers) are predominant in determining tone, anyway. Fender's web site has a FAQ where they reveal that SRV's tone was a result of "power tube distortion". All this time I thought it was because of his fingers and his playing ability.