Ya know, I read cylinder head and just assumed that he was refering to the cylinder itself. I guess my response sounded kinda silly for a cylinder head :)
I would agree with the other posts in that a new piston would be needed and that there would be no significant gain if the old one was in good shape. The replacement of the rings along with the other two parts is a gimmy I guess.
I think that the determining factor would be the price. I wouldn't pay full price for something to just set on a shelf and never use but if I had doubts about the integrity of my current cylinder/piston, it never hurts to have a spare.
If you get the cylinder and also find a new piston with rings at a great price then you can have a quick fix as a backup. If the old parts fail then you will not have to wait on the machine shop to turn your old cylinder and wait on shipping of an oversized cylinder. Just take the bad one out and intall the new one. If you want to after that, you can get the old one turned at your leizure and purchase the oversized piston at your leizure. Although, the moped shouldn't go through cylinders and pistons.
***Remember to go through the break in process if you do replace the cylinder and piston with some new rings!!!******