I just got Sandstorm. It's a pretty cool splatbook. It's especially relevant to Dragonmech because it contains earth-based attack spells, and, what's more, a creature.
...Called a Sand Dragon.
Seriously, this critters are awesome. Their breath weapon is an earth-based spell from the book, and the CR for a Great wyrm is 27.
...which, if I'm not mistaken, is also the max for lunar dragons.
So that means the terrestrial dragons have, among their numbers, some who can fight back...
Or maybe a campaign revolving around the mortal discovery of sand dragons and trying to persuade these Chaotic Neutral, survival-focused creatures into helping fight the lunar invasion.
So, yes, I'm glad the local store is starting to unload some 3.5 books in preparation for 4e.