When I started my layout over 25 years ago, the only decent metal replacement wheels available at the were Kadee. I had a raft of freight equipment kits, the majority being Athearn Blue Box kits. Many of them were undecorated that I custom painted for my own railroad.
As track was being laid, these kits were being assembled at the same time. I did have a dealership with Walthers so all of my equipment either had the wheel sets replaced with Kadee wheel sets or the entire strck replaced with sprung Kadee trucks. Kadee couplers were added to everything of course. Intermountain wheel sets were not available back then. As soon as Intermountain introduced their wheel sets, I like many others bought them. I was really liked them and usually keep them on hand even though I very seldom buy any more rolling stock. Looks like I have enough (yeah right) for the time being. With the completion of the last yard, I find that both yards can be crowded with freight cars, 20 some industries full of freight cars and still have enough to make up two trains held in hidden staging tracks.
Replacing plastic wheel sets with metal are probably one of the best investments for your rolling stock.