Exchanging Meso for Maple Points

Just make some changes to the items in the cash shop. Make it where you need prepaid NX to buy the more valuable stuff, cubes, pets, pam's songs, shielding wards. But still allow you to get stuff like clothes, resets, faces, stuff like that.

Since when aren't resets valuable stuff?

Also, if you make Maple Points only useful for cosmetic Cash Shop items, you instantly make their use as rewards in web events, or as compensation for major foul-ups, meaningless.
If Nexon want to make cosmetic items available for large sums of meso, they can do that directly, either through an NPC in-game or by making a "meso" payment option in cash shop itself (you can already buy some 1 meso items in cash shop, for various quests, so the mechanism is there).