I'm curious what other rules you were using around spells, Darrin. Were you rolling spells randomly and using % chance to learn spells for magic users, or were players picking? For clerics, was losing spell access to divine disfavor a real possibility, or glossed over? I can see those other rules making a big difference to how powerful your rule would make them.
Also, what was the highest level you played to? I played a lot of D&D back in that era that never made it above low levels. Players would move or change jobs, or the GM would get a shiny new world or game, and we'd reset and always start at 1st level again. :/ I gather that wasn't universal, but I can't believe I'm the only one who encountered it either.