A DnD group I am a player in uses the houserule that at Int modifiers +3 and +5, you get one extra skill or tool proficiency. Obviously Wis is underserved in this system again.
I would actually suggest the opposite. Int modifiers at +3 and +5 seem to only further reward Wizards-who already would go for high Int-but provide no incentive to other classes. As a Cleric, I'm not going to significantly sacrifice dex/str/wis by spending 7 stat points to get 16 Int for a single proficiency. Might as well put int at 8...
Rewards at Int +1 and/or +2 would serve a better job at tempting players to lose 1 (e.g., dex) modifier in exchange for +1 int and a proficiency.
