I'm with the moving forward crowd... for TANE I use a Win 10 Pro 64 bit i7 6700HQ, 16 gig RAM, NVIDIA GeForce GTX 960M and TANE runs smoothly...
But I also still have a DOS, XP Pro, Win Vista 64 bit, couple Win 7 Pro (32 bit and 64 bit), Win 8.1 Pro 64 bit... these units I use to run older software like Trainz TS12 on the Win 7 Pro 32 bit unit. I have alot of software that will not run on newer units, so I keep the older units and they become legacy units. I retain them so i can continue to do my development work (and play older games).
I bought the Win 10 unit about a year ago, so when TANE / Trainz / 2018 / NEXT / or whatever it may be called comes out, i will be in line for my next PC. I try to buy a new PC (laptop nowadays) every 2 years. It is prompted by what I intend to run on it. The Win 10 laptop was purchased with TANE in mind. I still do my .NET / Visual Studio on the Win 7 64 bit unit, it does not need that much power for what I do.
So what does all this BS mean? Again I'm with the moving forward crowd. According to
Moore's Law you can't just sit back and think that technology will not advance, so you need to embrace it and move with it if you are going to follow Trainz into it's next iteration.
To the OP, I don't see why your crashed Win 7 unit can't run your TS10 and TS12, i would check into that more, and keep that PC up and running for those versions. You say you got it running, but can't get Trainz to work, must be something we could help with, if we had more details. If you get a new PC I would recommend to keep different version of Trainz on the different PC's. Once you get one loaded on a PC and you get it stable, why mess with success.