I'm imagining two best uses for these cards.
1)Beefing up investigators who already have 3 in a stat, such as Diana's strength, Luke's evasion, Jim's intellect, etc. so they can pass basic tests that don't let them use spells to swap stats - most notably those on treacheries or scenario cards.
2)Giving the option to commit out-of-class skills to Mystic staples for power plays. Deduction onto Rite of Seeking, Vicious Blow onto Shriveling, etc.