Gentlemen,
Well, generally the value of protos for games that did actually see release is far less then that of those protos that went unreleased. Usually they will fetch about 2 to 3 times the value of their released counterparts. Granted this can varry depending on the desireability of the game in question. But at the basic core of this is the simple fact that a proto for a released game does not interest nearly as many collectors and therefore it does not command that high of a perceived value.
I don't remember the exact numbers, but a Riding Hero proto was thrown on ebay not too long ago and it began with like a $3,000 Buy It Now and a $1,000 Opening Bid and received no bids. Then it was relisted (maybe even relisted twice) with a $1,000 Buy it Now and then a $399 Buy it Now. If I recall, it ended up selling for about $175 or so through regular bidding.
A Super Spy proto sold several years ago for about $30. And Ray Young unloaded the rest of his released protos such as Viewpoint, Alpha Mission, and some other ones. Again not with much fan fare or interest by the community. If I recall correctly, Vinh's protos include Last Resort, Baseball Stars 2, and Kizuna Encounter. These seem slightly more interesting but again it is a matter of how many people really care about them and how much are they willing to pay for them.
Also for the record, some released proto carts do actually have value for another reason, but I won't get into that here.
