First off, whoops on that lame Mazda "fcuk-up"... yes, I meant RX- 8.... sheesh.
To address your ?s on the outgoing A4 1.8t ... the 2001 Edmunds guide put the AWD models at $18K, the FWD at $14.8K. No major issues that I know of, but I'm not sure how much additional hp the Haldex center coupling on a Quattro could handle.
Total Audi Performance would be good people to talk with; I consulted with them on the H&R coilovers for my father's A6 2.7T... talk about torque...:naughty: