I still build stuff for my favourite computer which was 8-bit from the 80s. I owned Amiga's after that but they did not give me the same feel. For me to stick to those massively underpowered computers seems to be that I find the hardware more interesting; with my limited free time I still understand all the hardware and can extend it, work on it; you can create mostly anything with 74series ICs and understand why it works after that. The closest comparable experience are FGPA/CPLD's but 74series are 'free' (you can find cubic meters of them on boards at your local garbage disposal or 2nd hand market or almost free on 2nd hand sites) and they look much better :)

This goes for the software as well; I understand that system in and out and I can build a simple OS from scratch (in assembler or C) and low level demos from scratch in days. The limitations make it interesting what the possibilities are; being clever with assembler and hardware can lead to very interesting results 'formerly not possible'.

For me the best 8-bit example is the actively developed; http://www.symbos.de

Then again; I would not know why you would make new hardware instead of going for the originals; it's not really the original feel / idea at least for me.