I pretty much agree with everyone already, but I have a few additional thoughts.
If you know that you will eventually move to another home, then you must also think of what is more important to you - time on market or sales price. Since you have already accomplished major renovations, then it may be that a 2-car garage will put you over the average sold price per square foot .
But if most of the homes in your neighborhood have 2-car garages, then adding the extra garage space may very well result in a quicker sale for you, which allows you to move on with your next plan.
I always tell my sellers - and buyers - that there is more than a monetary value to most real estate transactions.
If you add the garage now and you enjoy the added space and comfort it gives you from now until you sell, then it has "earned" its perceived value to you. Of course, if it also devours your savings or throws your ratios off because of added debt, then the expense has little value.
Please research the market value of your neighborhood, determine your motivation, and come up with a long term plan that will offer you value in a number of positive ways.
Hopes this helps.