Prior to 20xx version MP has always affected the damage to NPCs done by mages. I don't know if they changed the formula somehow, which would be kind of stupid because it completely removes the stat from the game in theory, but if they didn't then it should definitely boost your damage against bosses. Hell, I recall a friend of mine got a +8/15 MP paper set just to kill harpies faster back in the day.
Edit: Seems like the MP mechanic is kind of unclear to some people still so might as well explain it here.
MP gained from stats increases your overall damage to people and monsters. Stats are capped at 255, which can be reached by every single mage even with 160 points in INT. This is the main reason you no longer see the old school paper mages. Now, the additive MP stat inside the brackets (+123) does not affect damage in PvP, but it does boost damage in PvE, which is why it is one of the most pointless stats in the game, except for reasons such as solo farming or solo boss killing.
tl;dr
Main stat bonus 255 - Works in PvP and PvE
Additive stat bonus (+123) - Works only in PvE
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