I am wondering if it might make your house look more symmetrical, which is a good thing.

However, I think you need either an engineer or an architect or both to say if this sort of thing is feasible. These things are more complicated than they look, foundations, and all.

Please find out, including labor and permits, etc. what the cost will be, and if it is worth it for you, versus buying elsewhere a house that already has the number of rooms that you need. (Unless this house already has lots of land that you can't get elsewhere.)

I'm not an architect, but I can't imagine how you could add a larger garage with a full second story onto a split level home and have it look right. Do you have enough land to go further into your backyard? If you do, increase the size of your garage to two car and put the master bedroom behind it. Otherwise, I think you should consider moving. We were thinking of doing a substantial remodel to our first house because it was a great location. After spending a fair amount on architectural drawings and getting bids from contractors we decided the project was not financially a good idea (we would never get our money out of it), so we moved. If you do stay and remodel, remember what they say about not over-improving for your neighborhood. That's one reason people don't get their money out of a remodeling project. If everyone else still has unremodeled split levels, the value of your house will not increase very much even with a master bedroom.