A couple things..
1. The cheapest car to own is the one you already have, no matter WHAT car it is.. unless you own some exotic that's costing you thousands of dollars every month to fix and maintain.
2. Selling your car will cost you money. Explain, you say.. OK, I will. Your car is worth more to you than it is to anyone else because you've already paid x amount of dollars for it. What you've already paid plus what you'll get for it will not add up to your original purchase price plus all those lovely fees (taxes, tags, documentation, dealer extortion, etc.); most likely, it'll come up short by thousands. Those thousands could have been better spent in getting the most out of the car you have.
3. You seem worried about how other people view the fact that you drive a Scion. Maybe it's time to stop worrying about stupid stuff.. no offense. Worry about how things you do may harm other folks, taking care of your friends and family, the future of your country, etc... those things are worthy of your consideration. How others (except for your wife or parents if you're still somewhat dependent upon them) view your choice of car (including me) shouldn't even register on ANY scale of "things that matter."
4. About the only thing you typed that, at least to me, IS a justification for making a change is your musings that you might just be bored with the FR-S. Could be. Driving straight roads is pretty boring, no matter WHAT you're driving, at least to me. Maybe you need to move?
In all seriousness, if you really don't dig the FR-S for your OWN reasons, and it's worth taking a hit of $5000 or more to sell it and buy another car (remember, taxes and fees you've already paid that you won't recoup plus depreciation, and THEN taxes and fees on the car you'll have to buy to replace it, blah blah) there's nothing stopping you.
Personally, if I was going to be driving boring roads, I'd just as soon do it in a car that gets great gas mileage and has some fun factor. The FR-S works for me just fine. I guess there's something to be said for sitting in a quiet car that feels like you're home in your living room recliner, listening to your favorite tunes in relative tranquility, but that's never been my taste in driving. Everyone's different. Do what YOU want, assuming you can do so in a financially responsible manner.
Somethin' like that, anyway. Good luck.
Barry