One of the things I really liked about Vance's system was specificity. I would have magic-user players tell me, "I'm memorizing three burning hands today." And I'd say, "Okay, Jabberwocky's a short poem. I want you to memorize Jabberwocky before next session, but I want you to memorize it twice, in different parts of your brain." I got the point across. It encouraged caster players to find similar spells with slightly different effects that were nevertheless different spells. It only works if the GM actively makes sure there are alternatives that can be found.