+1 on putting the bike(s) inside the car unless you want to take a hit on mileage. Even the bare rack on top of the car will increase air drag a bunch, meaning a fuel economy hit. That seems to point to the TDI, but I've never had one so I dunno. A TDI Transporter would be great, but they aren't available in the U.S.
My wife and I have been shopping for a "new" car (the 2003 Toyota has 150,000 miles) and we're thinking about a Nissan Altima hybrid. A little bigger than what we have now, and better fuel economy to boot. That and a hitch rack would a reasonable alternative for you.
__________________
Jeff Wills
Comcast nuked my web page. It will return soon..