Good idea with the Avenger, Falko! And yes, I could make a big workshop pretty easily... If I had the time.
However I'd rathe leave the Avenger as it is (except for vastly increased economic challenge, like you said) and add some less-OP craft as the "ultimate non-Cydonia craft"
However #2, to make your idea work we'd need something like 3x3 workshop with 1500 or so capacity, and make Avenger require 800-1000 space, else you could easily meet the space requisites for the Avenger with a block of 9 normal workshops.
9+12 (3 large quarters)+3 stores+4 (hangar)+lift = 29 tiles out of 36, pretty much a whole base dedicated to the space program