I would not buy it. There is a good reason for not buying it. I own the 3.0 version and I run a 3.0 game. Otherwise, if I ran a 3.5 game I would buy it in an instant.
Absolutely. In fact I ordered the 3.0 original a little while back from an on-line used books store and instead got ToH III. It's also a great book, but I really wanted the first one, dammit! And a .pdf that just shows errata to v.3.5 isn't good enough for me.