"I seem to recall the plus 4 was often referred to as the minus 60..."
It was a bad executed attempt to make a business computer out of the 64 architecture. Despite some hardware improvements (i.e. more memory available) they removed some of the most useful game features, and added "4" (or better 3+1) limited office application in ROM.
Despite its more modern look (and better layout for cursor keys), it wasn't good for games like the C64, wans't compatible with its software, nor good as a business machine, its wp, spreadsheet and database application were too limited.
I know it very well, because I got one. I couldn't play much, so I had to learn programming instead <G>. One nice feature though was its built-in "monitor" application, which opened to me the realm of assembly and low level programming...