The goal is not to have the sites 100% connected in the end. This will be a tight knit community of E90 drivers and E46 will continue to be a tight knit group of E46 drivers.
The best way to drive traffic here at first is to post about it when people talk about the E90 on E46.
Seeing how the E90 has only been available to purchase for less than 1 month, I think this site is doing well.
Tim