I assume your Infiniti is the G35x and not the M35x or M45x? What's your loan's interest rate? How much are you paying for insurance (and how might this compare to an economy car)? Do you
need AWD?
I estimate you're spending $730/year on fuel. A similar year Honda Fit would be around $400/year. A Toyota Prius could be about $260/year. So you could save $330-470 per year on fuel by switching to an economy car. It shouldn't be impossible to find these or similar cars for $7k or so.
Assuming about 12% depreciation per year, your $11k Infiniti will lose $1,320 in value over the next year while a $7k vehicle would lose around $840. Over five years the Infiniti would lose about $1,890 more in value (or ~$380/year).
Assuming your loan has a year remaining and is at 3% interest, you'll pay about $50 in interest over the next year.
The Infiniti G series cars are
extremely reliable, so I wouldn't be too worried about maintenance.
Another thing to consider is your personal negotiating skills. How confident are you at selling your car for what it's worth and not overpaying for its replacement? You could lose some money upfront by making a switch, especially if you buy/sell at a dealer instead of privately.
In total, you're looking at being able to save $760+ per year. Depending on your finances and goals this could be significant or it might not matter to you at all. I personally don't think keeping the Infiniti would be a wrong choice (depending on your finances), but there is money to be saved if you want to go that route.