I'd only be onboard with this if the game stayed colorful and anime-style. None of that gritty, nasty, gray/brown wannabe realistic crap. A game that looks like it needs a bath is only aesthetically appropriate for horror games, dark fantasy, and shooters. Maybe I'm biased because I came up in the 16-bit era, when most of the biggest games of the time used bright, vivid colors and cartoonish art styles, but I never really got on board with the whole "the realer the better" graphics bandwagon and never got how making a game look dirtier made it somehow "gorgeous."
So, sure, update the engine, upgrade the combat, smooth out the graphics, sharpen the textures...but keep Mabi colorful and anime-esque. Maybe bring in some crisp, clean cell shading. But please, don't dip the game in the same bag of dirt as half the AAA games from the past 16 years.
I agree with doing something about CP-based training requirements. They make certain skills a bit annoying to train...particularly Windmill. Why? Because not only is it heavily CP-dependent, but it also requires you to hit/kill 4 or more enemies of a particular power class all at once. Sure, training in Shadow Missions (particularly Their Method) helps. However, the tedium of creating a party of 1 to be able to pile up KOed enemies in range of your attack, then trying to pile them up at a quick enough pace that none of them disappear on you, and Goddess forbid if you hit a target too close to one of the piled ones or defeat one and knock it slightly out of range! And don't even get me started on what a pain it is finding field enemies that fit the training requirements and appear in big enough groups and close enough clumps to be useful once you're strong enough that the first tier of Their Method provides you with zombies that are of equal CP to you but then the next level has Awful-level zombies when you need Strong!
Having enemies stronger than a requirement's stated CP requirement count toward skill training would be a big help, as would changing the wording on those multi-hit requirements from "several" to "four or more." Right now, the wording is really vague and confusing for a new player. Combine that with the aforementioned annoyances finding suitable enemies to train against, and...well, there's a reason why Windmill is cited by many players as the most tedious skill of all to train. Anything that would make that grind less soul-crushing would definitely help retain newer players.