Limited resources and means, you know, promote creativity. Programming a modern standard computer nowadays is quite available to average Joe and Jane. That's why we have tons of crapware. But, forcing them to program a less common, sophisticated, complicated or limited architecture forces them to adapt and into being more creative. This serious game is quite a good example, and, I suppose that was also the intention behind it.
MSX's are hard to find in Brazil? I thought it used to be very very popular there. I see many of them here [0] for prices I would definitely pay; here it is very hard to find them for those prices still. I would buy stuff like this [1] or [2] blindly. If you buy it I will pay you more + shipment to me :)
C64s are still ok to get in other countries; MSXs are getting scarce. I managed to collect over 100 of them luckily as it is my favorite computer (nostalgia sure, but I also find it important that young people can see how it used to be).
I have all the computers you name there, several of each; I can trade you for a working Gradient or Hotbit. Or just pay you :)
Personally I like the ZX Spectrum & MSX the best to code on, because I was raised on Z80 assembly. After that the Amiga, but I already find that a bit too advanced; MSX is so limited (a little over 3 megahertz & usually 64-128 kilobytes! of RAM) it really is a game to get things working at some speed. But people are still doing it; for me the highlight is [3] which I find far more impressive than the latest JS-soup framework :)