I agree that the Earth Elemental thing is handy, and a useful addition to the bag of tricks (and if there's anyone who ought to have a wide and varied bag of tricks, it's a factotum//wizard). I just don't think you should rely exclusively on it, because there are traps that it won't pick up. I don't know precisely what's in the Tomb, but it's famous for having a wide variety of traps, and I can think of at least a half-dozen different categories of traps (all of them including nonmagical specimens) for which the elemental would be useless or worse. It seems a very foolish idea to assume, a priori, that none of those half-dozen different categories shows up somewhere.