Any ball can be resurfaced to like new, and as Jason said, polyester balls are most definetly the easiest to resurface. However there is a limit of how much material you can remove from the balls outer casing before you start to reduce the balls diameter which will affect how it is handled by the ball return system of the machines. In a Brunswick equipped house you may experience ball return problems with a ball that has a reduced diameter sooner than a AMF equipped house, on account of the different design of the ball return systems.
If you resurface your ball regulary, or try and remove a deep gouge by taking off a heap of material, you will sooner or later experience a reduction in the balls diameter, if you try and remove a deep scratch or gouge over a small area of the ball, you will create a flat spot, it may not be obvious by sight or by feel, but any material taken from the balls outer casing in only one area is going to cause a flat spot!!
If your ball has deep scratches or has been gouged, unless the scratch or gouge is on the ball track...........let it be!! your doing yourself an injustice by taking any material from the balls outer casing, the integrity and the roundness of the ball will be affected, depending on who does the work for you, you could end up with a ball that looks great but won't roll like it used to or should.
If you have a deep scratch or gouge on your ball in the ball track area, the best repair is supa-glue............clean out the scratch with some metho, make sure the scartch is clean, dry and free from oil, squeeze a few drops of supa-glue into the scratch, be sure you dome the glue over the scratch, the supa-glue will shrink slightly, this also allows any air bubbles to settle in the portion of supa-glue above the balls surface and also give you some material to cut back and polish..........give the glue at least 4 - 8 hours to dry, (the longer the better) take a smooth file and gently file the glue back, be carefull not to let the file hit the balls surface too much, keep the file moving in a roundish movement so as no to cause a flat spot on the repair...........once the excess glue has been removed you can go through the different grades of wet and dry, be sure to remove the scratch marks of each grade of wet and dry before progressing onto the next grade.
You can of course skip the filing step all together and just use the wet and dry to cut back the supa-glue, this way there is less chance of you making a mistake, it doesn't take much to cause a flat spot with a file.
To gain maxium holding power of the glue to the ball, you may need to "key" the supa-glue into the ball, by this, I mean, drill some very small holes into the ball inside the scratch on a angle away from the scratch, back into the ball. This is most definetly required for scratches that are shallow, if you don't do this, you run the chance of the repair falling out in avery short time!!
Unless you are completely confident of doing the above process, my advice would be to take your ball to a competent pro-shop operator.
I do hope that the average or novice bowler has a better understanding of the process for repairing ball damage and the consequences of resurfacing a ball to often or to aggressively.
Also understand that your throwing a plastic ball at 30 pounds of pins, the ball is being returned to you by a huge mechanical machine made of STEEL, you have to expect the odd scratch here and there.............it doesn't matter which centre you bowl at, all balls end up scratched..................it gives them character............
If you require more information on the ball repair process or don't fully uinderstand my post, you can post back here or contact me via private message.
Neville