I found a ART MPA Gold Dual Pre for $300, used, at a local shop. I know they go for close to $500 new, but is it even worth $300?

No, it isn't. The Gold series is notoriously poorly built (even worse then most ART stuff). I'd save up and buy something a bit higher up the scale.

I can't speak to the ART pre's, but i really like their compressors (like the Pro VLA and the TCS) and both are cheaper compressors, but good deals.

Other then those ridiculous weird lil tube Pre amps that they have flooded ebay with for $50, i find there stuff to be fairly solid.

I like the MPA, at least in terms of a preamp design. I won't go into all the technical details as to why I like it, and I can't speak for build quality. I've got a nice modification for it that I'm going to be putting up on my website soon, if you're interested in that.

The cool thing with the MPA is that you can sub a 6GM8 for the 12AX7. For those not in the know, the 6GM8 is a 9 pin dual triode, just like the 12AX7, except that maximum plate voltage is 45 volts. That means you can get rid of the blah sound of the starved plate 12AX7 that greatly limits the character of the preamp. The MPA Gold has switchable plate voltage, and I'm not sure what the voltage level is on those--if it exceeds 48 volts, you can't use the 6GM8.

Anyway, if anyone is interested in the modification, let me know.