Yes, BASIC 3.5 (264 machines) and BASIC 7.0 (C128) were further developments, as well as the unreleased 3.6 (LCD) and 10.0 (C65): http://en.wikipedia.org/wiki/Commodore_BASIC#Released_versio...

AmigaBASIC was indeed a bit of a lame duck. I used HiSoft BASIC myself, which was backwards compatible but added a lot of features, including a compiler.