Some good comments above, a change in direction is as much as a reason as "upgrading", i went from an rx7 with 500hp to a 350, it was painfully slow and cheaper in comparison but in many other ways it was far far superior to the Rx7 even though it cost less, so i wouldnt say it was an "upgrade" but it was a better car for me at the time.
If the op has lost the love, not a lot will bring it back and often having something else is the only thing that will, i tried loads of other cars when i was into Rx7's when i lost the love, v8 soarer, mx5 bbr turbo, evo4 but always went back to rx7's, until i got a 350 and never looked back, until i wanted a change recently.
Unless the op has thrown huge amounts of cash into it and i dont mean a set of wheels and a bumper, whats the worse than can happen, they are hardly rare or desirable to the point you just couldnt go out and buy another and as long as you buy and sell at the right price, you probably wouldnt even loose any money