With the spectrum card you should have seen $1200 to $1400 for even a BIN!
I think that's too much with just the 3640 accelerator. $800-$1000 is about right, maybe a little more for being so clean.
$400-$700 Base 4000T with 3640
$100-$200 Spectrum
$50-$100 Hydra
The other trinkets, setup and condition no doubt added more but it's more difficult to estimate the luck and like aspects

.
Is that because of the passthrough or just the fact that it had an RTG card?
The Spectrum passthrough is nice but a Cybervision 64 can be bought for not much more and is way better performance.
Nice job btw. Your presentation and reasonable buy it now price and shipping made for a quick sell. You might have sold it for a little more if you weren't in a hurry but I think you did pretty good.