Hi nick
Your idea of actualy changing the transmission from an AWD to a FWD transmission is actually a breath of fresh air.
Most people who want better mpg talk of just installing the FWD fuse.
Where I live, with the winding roads, and bad roads, and snow, and rain , and fox/deer/ wild turkeys
etc., awd is a HUGE advantage to an old speed freak like myself!
Its YOUR car, do what you want.
Just realize that once you make it your own , the value is "subject to personal interpitation."
ps, pump up the tires, wax it, tune it, keep off of the gas, take any extras out of the trunk, and drive it like you have no hormones and your mpg will rise.