Which scale do I have?

[CNE Runner]

Like Jim (and others) I have used 600 grit wet & dry paper on model railroad rails for more years than I care to count...all with no problems at all. If you use one of those rail cleaners (such as a Bright Boy), follow it up with the 600 grit and use the wet & dry paper after that. A product, like a Bright Boy, does polish the rails - whilst the 600 grit paper burnishes the surface (and doesn't leave minute scratches - which trap additional grunge). Over the years I have used Wall's clipper oil as well as LaBelle products after the wet & dry paper. The conductive oil shields the rail surface from atmospheric pollutants and is supposed to keep the rails cleaner longer. I don't use any oil anymore...the choice is yours.

Oh, be sure to burnish the inside edge of the rail as well as the rail's top surface. Much of the electrical contact between the rail and the pick up wheels is from that inside surface.

Ray

[mabloodhound]

I've got to buy new track anyway because I don't have enough curved pieces to do anything with. Is the new track still compatible with the old track and those little connectors? And can you still get the little connectors?

The new EZ track won't really work well with the old track (it can be done but not worth the trouble).
Look on e-bay for used EZ track.   Prices are good because people sell these when they set up a regular layout.   The EZ track includes a plastic roadbed under the track which also makes it look better.
Buy a complete oval to start with for your son.   Then add to it if he likes it.

[SteamGene]

Uh, to combine EZ-Track and regular track one needs some cork "ballast" and a saw or blade to cut off the plastic ballast clips from the EZ-Track where it meets the regular track.  Cork goes under the old track.
Gene

[Joe Satnik]

I'd rather trim out the cork than cut off the trackbed tab ...color a gray tab black or dark brown with a magic marker to make it blend in with the cork....

Joe