Well, Melanthe, your analysis is pretty sound. I've had mixed results with asking sellers about the amounts of their reserve bids -- some will tell you, most won't. What you *can* do, and ought to do whether you ask the seller or not, is go to the seller's history and look at his other reserve auctions. There's often some relationship between the amount of the reserve and the value the seller places on the item. Sometimes it's the amount he paid for it, for example. But if you look at his closed auctions where a reserve was involved you often can detect that relationship even if it's an unintentional one.
This approach also offers a safeguard against the unscrupulous sellers who deliberately set an impossible reserve bid, then approach you privately after you've been the high bidder but not met the reserve and offer the item to you for some price significantly higher than your "winning" bid. This is an illegal procedure and eBay jumped on the last one I blew the whistle on and had him out of eBay within 2 weeks.
My slogan is, "If there's information to be had, use it."