What's Warriors of Mars worth to me? In terms of money, it's worth the $5 I paid for it a few years ago. It's a perfectly good reading copy if you ignore the staining I described for it on one of the two valuation threads (the stains seem to not impact the readability one bit, lucky me).
What's it worth as a roleplayer? Immeasurable. It's one of two licensed games dealing with Barsoom, the other being produced by Heritage Models. As a "proto-RPG" (according to one source) some of what's in the book also made its appearance in a more finished form in Dungeons & Dragons. In looking through it, the most recognizable things in it were the award tables provided for killing creatures and the concept of hit points.
While the Heritage Models Barsoom
RPG was better produced, Warriors of Mars was FIRST, and that's what counts. Is it worth the $350-$450 range it's been going for lately? Not to me. The amount that was paid for on this auction is reasonable for something with the perceived scarcity of this item. Especially given that it had only one printing before being pulled off the market due to objections from the ERB estate.