I view Mario RPG stories as Saturday morning cartoons and I do think adding voice acting really makes it pop. Good voice acting can sometimes even make a corny script make you laugh, just by the delivery of lines alone.
I'd honestly prefer to get a TV adaptation of the Mario RPGs that adds full voice acting over voice acting being added to the games themselves. As for full spoken dialogue from Mario and Luigi, I'm very mixed on it. Charles Martinet has never given a bad performance but I do think the times he's done full voice acting for Mario and Luigi only work in silly unserious contexts they're intended for. I think a voice direction like that of the movie is better for a dramatic story like one from the RPGs. I don't want Chris Pratt doing it though. Charles Martinet's portrayal of Mario's dad proves that he could have done Mario with that voice direction. If Kevin Afghani does it, I'd hope he takes it in a similar direction rather than just doing his version of Charles's game voice in longer sentences. That just isn't a voice direction I think works in full dialogue for a dramatic story driven context.
An example of something that's already whiplash when in text form, is Luigi responding to Grambi's heartfelt plea to save the world, which comes right after his daughter sacrifices herself, with "okeydokey." In moments like those I'd like to see Mario and Luigi actually show serious emotion and elevate the intended mood rather than be goofy and turn it into parody. Usually, Mario skirts it by being a silent protagonist and Luigi has dialogue that makes sense in that scenario, but in that case it feels like he randomly turned into his portrayal in M&L or Mario Kart and played an unfitting voice clip instead. Bowser is usually balanced perfectly for scenarios like these, since not giving a shit about the plights of other characters is part of his personality, and so him making wisecracks doesn't really take away from the plot at hand (nor does him roasting the new villain make the latter any less of a threat). Mario and Luigi are characters you'd expect to have empathy and be able to read a room. So having them play one of their sillier voice clips, or have a piece of dialogue that evokes the thought of one, after a scene like that doesn't work. If that scene was voice acted in a cinematic setting, I would not want Luigi to play an okeydokey voice clip there, amusing as it would be divorced from the story.
I think it's the fact that I genuinely hold real emotional connections to these stories and don't want them to be completely parodied by having too silly a voice direction just because the Mario brand usually goes for that. But I also don't want voice acting that tries too hard and sounds fake as a result (how i feel about the Fire Emblem voice acting I've heard in Directs). Ideally they would have voices that are cartoony enough to fit an animated movie, but not to the degree that the story can't get serious and work. The balance just feels too narrow for the risk to be worth it imo, and I don't think Nintendo is ever gonna match fan renditions here. Just in terms of Bowser portrayals, specifically for musical numbers, Peaches is fine enough but I think Man on the Internet has several Bowser songs that better capture the energy & vibe I think he should have, especially MOTI's Adventure's End with lyrics that might just be my favorite Bowser villain song ever with how it takes an already epic instrumental end elevates it with powerful lyrics that make him sound like a god, with Mario and Luigi also joining in to oppose him. (Though their vocals, while they work for that song, like i said before I don't think the voice direction established in the games with Charles Martinet, and now with Kevin Afghani continuing it, is a good fit for a fully voiced setting with a serious story).
I mean Nintendo has (rarely) struck gold with full on voice acting before, King K. Rool's voice in the DKC cartoon is perfection imo (the writing is another matter). But of course that didn't stick. I still read his dialogue in DK Bananza in Ben Campbell's voice, but it's clear his canon voice is deeper & more beastly kind of like Bowser's, which if it was used in full voice acting I'm confident I'd see it as a step down from his past portrayal.
