I wouldn't move them until I did a few things:
1. Draw a layout of every workbench, stationary piece of equipment, portable piece of equipment, refrigerator, sign, battery charger, TV, stereo, computer, etc. and anything else that needs power.
2. Figure out the mounting height and power requirement (including plug type - NEMA configuration) for each item.
3. Make a list of anything you know you want in the future and allow space for it.
I've found that running a piece of plugmold across the front of a bench is the most effective way to have accessible power without constantly fighting cords across the work surface.
48" to the center of most outlets should be ok unless you want to be able to stand a sheet of plywood or sheetrock on the floor in front of them. I'd go with 54".
Common sense says to make everything that is not hardwired into the garage a GFCI circuit either by device or breaker. It's a garage - things get wet.
One thing to add to what Steve said. Include at least one receptacle in the attic.
Don't know if the garage is attached to the house or not from what you've said, but I'd consider adding a few to the outside near the soffit if you put up Christmas lights.
I'd also make sure there was at least one receptacle near the driveway.