Go for a decent CAT 1 replacement to be honest, but you won't save that much on the insurance though.  Piece of mind however is priceless.
AFAIK no one manufactures tubular manifolds for the MK3, you could probably get one made though (£Â£Ã‚£'s).  As far as exhausts are concerned there is a good post on the ClubGTi forum, there was quite a discussion on this.  Basically, STD or very close to std bore size etc works the best.  Been tested in magazines and only 1 in 10 showed a slight improvement.  Show or go??  Thats the choice.