I like the look of the retro Spectrum very much - they 've down a really very nice job. Its form-factor with everything built in to a keyboard is conventient much like the original BBC B, Commodore C64 and the many others of that era. However much like the Rapsberry Pi, it is a niche product - which isn't to say that it won't be successful and enjoyed by many.
The early 8-bit computers' popularity came in no small part due to their utter novelty and price point (compared to 'real' computers). However, these days most homes already have a home computer and it's in the form a PC or laptop or tablet. You suggest the need for a 'more focused machine' but I'm not clear on what that focus should be.
I still have my BBC B - it's kept warm, dry and safe in a cupboard, purely out of nostalgia, yet, despite my affection for the BBC, I will never go back to using it. For everything else I have a PC that in real terms probably didn't cost a lot more than the BBC-B. This PC allows me to program, make music, write, edit photographs, stay in touch with friends (...I could go on...), so I'm really not sure what you are wishing for.
Time has moved on and much like the penny-farthing bicycle such computers have been consigned to history for everyday use. ymmv.