"Value". What is the value, do we reckon?
On the surface (because I cannot go into depth on this stuff like the big boys...) the price of $2500 is not too far out of line with what is listed in lots on the high end in ebay.
BUT...in the real world, does one need a bunch of early track, controllers, powerpacks, & etc.? I fiddled with early aurora track connections a bunch as a kid, and imo, they are not as good as late model AFX. Steering wheel controllers are rough to operate quickly, and the wheels break off, and so forth.
Which leaves the cars. There are a bunch, but what would a potential buyer (potentially Nurmix) do with them? As MM points out, use 'em, bruise 'em, and the value plummets. Would some of them be runners on newer chassis and the rest be in "a collection"? Is that "worth it"? I would suggest it is a subjective thing.
Even if one can verify the value, is it "worth it" to you?
Probably a lot of it could be flipped on ebay if one had the patience and jumped through all the ebay shipping and whatnot hoops.
Also, almost everything is negotiable. Almost, one never knows. If I decided that it was "worth" $2500 and/or "worth" it to me, I would start the bidding by indicating interest and asking if the seller was interested in a cash offer. If the response was "yes", my next round would be to indicate that but I was definitely interested and would be willing to make an offer--but that I didn't want to hurt any feelings, . If the seller responded positively, my first offer would be $1250-1400. With the goal of buying eventually for $1700-1800.
Food for thought.
ps--Just remembered. In 2003 or so I spotted an '89 Dodge Ramcharger for sale. Not mint, but not rusty. Coincidentally it was marked $2500. I went through the steps above, counting on the same $1700-1800 purchase price. I offered $1250 cash--and the buyer accepted. It's parked right out front. One can never tell.