Generally speaking, model wheels are seldom made of steel. Usually, it's the axles that are steel, and that are attracted to the uncoupling ramps. This problem has been encountered in HO, but to a lesser extent because the axles are higher off the rails. However, in HOn3 it becomes more serious and similar. Most folks looking for magnetic uncoupling in HOn3 end up hinging under-the-track magnets or using electro-magnets to avoid the unwanted uncouplings. But that doesn't solve the steel axle problem during uncoupling operations.
As I hinted at earlier, I'm not in N, but Kadee and NWSL make brass wheels and axles in HO/HOn3 for exactly the reason you talk about. Brass axle with nickel-plated brass wheels are plenty strong and durable enough, especially for N. If Roundhouse/Athearn was chincy enough to use steel axles on the tender wheel sets, chances are they are a fairly standard size, and a suitable replacement ought to be out there. I've heard great things about the NWSL folks - they just might be able to fix you up, and it might be a worthwhile product idea for them. Also, contacting MicroTrains might be of use - they should at least know of the problem, and might even have a solution.
Using phosphor bronze strips or tabs for electrical pickup, either against the back of a hub insulated metal wheel, or as a slider directly on the track is a great idea for small engines anyway - another fairly common practice in HO on small engines.