Hi michaeltaylor - I don't want to sidetrack the conversation, and I am afraid I don't have anything to add with respect to making plastic minis (other than, perhaps suggesting laminating the minis, or finding clear plastic 'sleeves' to slip the minis in?) but I have to ask for my own curiosity. What did you print the paper minis on? I've got thousands of paper minis printed on 110lb cardstock and (even better) matte photo paper, and only in rare circumstances have I had a mini suffer any damage.
Welcome to the forum, and I hope you find out what you need!
Here's an option - if you can find a plastic "base" to affix stickers to, you can print the minis to sticker paper... Along the same lines, when you assemble the minis, you could sandwich a piece of cardboard between the minis, then cut them out, making them much stronger.
You can print any paper miniatures onto printable clear plastic sheets using either a laser, or an inkjet, home printer (you'll need different types of special plastic sheets for the different printer types). However, they will end up transparent, and the plastic doesn't really fold over like paper too reliably (probably best to cut the backs and fronts then fasten them together later). You can add some plain white paper/card between the two clear plastic layers to improve the opacity, but the colours may still look quite pale and washed-out.
This is though not a cheap or an easy option unfortunately, as the printable plastic sheets are expensive compared to photo-quality card of suitable weight (about 110 pounds, or 200 gsm, paper/card is best for paper minis), plus it's more work and time to construct each miniature.
I have to agree with other comments here about the overall robustness of paper/card minis and buildings. I have a few card buildings of this type that still look pretty good after 35+ years of use, plus storage/sitting on shelves time, and several house moves along the way. It may depend what you consider reasonable wear and tear, though!