But if you want to have a game for retro platforms, better first code in or less capable machine - for example Vic-20 or Apple II and then improve it on the more powerful hardware like C-64, Sega Mega Drive or Amiga and add new ideas.
I would say opposite. It is much easier develop a game for Amiga 500 and then downscale features to 8-bit machines. I dont see problem there. Often C64 games were coin-op conversions and did better than games designed for C64 only. There is still people thinking Rob Hubbard's Commando is an original.
