I don't remember where the idea of using Pledge furniture polish on toy trains first came to my attention back in the 1970s, but I have used it on some of my vintage Gilbert AF trains, both tinplate and plastic since then with very satisfactory results.
All of my trains, whether MIB, Like New or well-loved and well-worn, new production or vintage, are available for operating and are expected to be run on a layout. I am, however, partial to the clean, shiny look of tinplate, even when the tinplate is plastic, and to traditional toy train layouts.
Accordingly, I have used Pledge as the final step in preparing those trains and accessories that come to me well-used and/or dirty for running or display. Restoring a shine to these items allows them to blend in better when displayed or run with more highly graded vintage or new production items.
So far I have not detected any damage caused by the polish, and the items so "restored" continue to look much better than when I aquired them.
As a side note on the removal of Pledge polish, back in the early '70s my wife went to polish our solid wood coffee table which was one of our few pieces of good furniture that we purchased new. As soon as she sprayed it on, she realized from the smell that she had grabbed the Easy Off Oven Cleaner instead of the Pledge. We quickly wiped the oven cleaner off and found to our great relief that we were in time, and the wood table top was undamaged. On the other hand, there also was no trace of old polish or wax build up to be found on the table top.
Still, unlike Pledge, oven cleaner is not a cleaning method I would recommend for our toy trains!
Cheers!
Alan