I don't know about you, but the first time I ran this the party of four characters which remained the same throughout the entire AP reached level 22 by the time they encountered Adimarchus. We agreed as a group to run things by the RAW and that's where we ended up. Epic level and everything, all the official WotC and Dragon Magazine source material for 3.5 was allowed which meant PCs had access to some pretty righteous abilities. It was an eternal fight which took an entire evening to be sure, but a total blast. When the chips fell the party had actually used up relatively few resources and from that perspective seemed rather anticlimactic. These were a bunch of min/maxers though. Things like extended greater spell immunity to blasphemy were SOP.