Do you know if the "leak in the wall" is the old galvanized pipe leaking, or, perhaps just the packing washer on the stem? If it is leaking around the stem, a new packing washer or a few twists of string packing on top of the old washer &/or a tweek of the packing nut may solve the problem. It looks in your picture like it might just be a packing washer.
If there is some disaster inside the wall and you have to open up the tile to get to it, change the valve. If you can work from the back, it is your call. Whatever you do to cover the extra holes is going to look a little goofy. If you are thinking of saving the valve, take it apart. If the washers are gouged or cut, look to see if the seat is replaceable, if they are not - change the valve or expect to change washers on a reqular basis. Look at the threads on the stem, are they square or have they worn to a narrow blade. If they are worn, you can expect the threads in the body of the valve to be in the same shape and you should probably change the valve because you are living on borrowed time.
If your house is piped in galvanized, changing just the section in the wall to copper is asking for electrolysis problems unless you plan on repiping the house in copper soon. There are code restrictions (that vary locally) on how and where you can transition between these materials. If you can find it, and afford it, you could change all the piping in the wall to brass, which would not be a problem (except the finding and paying part) whether you later repipe in copper or not.