definitely dont trade. the rx8 is certainly the better car, but its not so much better as to warrant an additional 30,000 miles and the loss of value between the two in addition to the aforementioned issues with trading cars with a buddy.
if you were trading for a corvette or a 350z or something like that, id say go for it, but not for an rx-8, your not getting much more car.
A woman goes to the doctor to figure out why she is having breathing problems...The doctor tells her she is overweight. She says she wants a second opinion...the doctor says, "your ugly".