I don't think they should increase MP costs of the spells, but it certainly wouldn't hurt to make them more useful. As it's been said, nukes are pretty much useless on most NM fights as they do such a tiny amount of damage. You literally dart for more than you nuke for most the time... And your nukes can be resisted pretty easily.

As far as NM's go though, I don't honestly see MP management being much of a problem. My shell has killed all of the NM's with 5-8 people with little problems (Most notable was my shell's 5 man Great Buffalo kill, sadly I wasnt there for that!), and as one of the main healers in the shell I can vouch pretty well that it is rather easy to keep MP up, especially after the MP regen update. I actually made a macro that casts sacrifice 3, then puts my weapon away automatically to help with my mp conservation, cuz the second the weapon is down you start regaining mp. This pretty much negates all the mp cost of the cure, and usually gains some extra MP back beyond the cost before i have to heal again. Of course i also toss up poison 2, dia 2, and bio 2 at every chance I get. You can also now siphon all NM's, until they run out of MP... Making it even easier.

So yea, MP management in this game is a breeze under any condition, but I don't think they should raise the MP cost of spells at all. If anything, they should introduce tier 3 nukes that cost more mp, but are actually useful. Currently, the only thing that uses up a sizable amount of MP for my thaumaturge is the application and reapplication of poison II. But even casting poison once every 10 seconds, exaltation is still always completely ready to use before i'm even at 50% of my max mana.