We just finished a garage sale where I was able to get rid of about half my stash. This amounted to about 100 kits of pretty much all types and kits. I managed to get rid of almost all of them, but -

Among these were a Monogram B-29($20); an AMT P-70($10) Night fighter and a Hobbycraft Ju-88($15). All in 1/72 scale. All are still in their original shrink wrap.

None sold. Was I asking too much, or what?

There's no way of knowing. Those look like OK prices to me, but you may be unlucky and live in a place where nobody wants to pay even that much. Or you may simply not have been visited by anyone who wanted those particular kits (which I think is the more likely).

An easy way to find out the current value of any item is to look it up on eBay. It aopplies only for as long as the item is available, and the price can change from example to example, but over time an average appears. And of course, flogging them on eBay may work, and may help you out if two idiots get into a bidding war on them.