3D printers would be nice to get one. As a model railroader, I’d use it to create one off items (maybe N scale NASCAR race, a few unusual buildings and boats) or maybe start a business creating model railroad items.
I remember helping my late father work on his HO set-up way back when. He got the magazines for years and I would read and re-read them.
They’re also great for repair/replace fixes for those critical small plastic parts that, if they can break, will break, will do so at the worst possible time and will make anything using them inoperable.
Don't want to rain on your parade, as I like seeing others experiment with 3D printing. But consider it a hobby, not a business. It takes a very long time to print each item on your 3D printer (unless you spend really big bucks). You may not recoup your expenses and labor! Then again, maybe you will build some really nice items for a niche market selling them for many hundreds of bucks. Have fun.
I have a couple of 3Ds on my amazon wishlist for someday.