People tend to say that INT is much more important for a Summoner than MND is for a Scholar. This is because overhealing is useless and SCH's strongest heal ignores MND entirely (Lustrate - heals 25% of target's max HP). However, there's no such thing as too much damage for a DPS class. So, if you plan to play both, you might want to just put all 30 points into INT. As a note, INT is totally useless for SCHs, and MND is totally useless for SMNs.

If you plan to main SCH though, having those 30 points in MND would be pretty useful for endgame content (right now, only Final Coil).