If you find something to be odd, well your opinion might be irrelevant to other people, with all due respect. Everyone shall do as he pleases with his own property.
You consider NT3.51, from 1995, a waste, and at the same time, you recommend NT4, from 1996, duh... big difference that makes in 2013 ;-) And how can you even mention win95 which is extremely unstable and crashes every 5 mins if used with "newer" software...
Having said that, I never said one should buy the latest i7 and install 3.51... but speaking from personal expericence, if you use a pentium 3 with 256 mb, divx movies, youtube, and firefox run unusably slow on 3.51, with a p4 and 512mb it's a lot better, never tried 1gb though.
You can use the old hardware "that it was designed for" as you say but then you will never be able to use the programs I mentioned, of course.
As for NT3.1, it is pretty well unusable nowadays, no hacks possible, I'm afraid.