If you havent read Chris Jericho's book(Around the World In Spandex: A Lions Tale), Id highly recommend it.
Jericho talks about his time in WCW, and how he was an AWFUL promo guy. I think most would agree that he's among the best in the business today. So how did Jericho get to be so good? Practice.
Jericho sat in, week in and week out, on a WCW portable studio called the Box. It was where all their promos were filmed for Nitro. Anyway, Jericho filled in one week when Lex Luger no-showed because he went tanning. According to Jericho, he SUCKED at first. But he sat in, week in and week out, honing his skills. He practiced over and over. He called it his personal "boot camp", and credited it for how he became the promo guy he is now. That, and through watching the greats live, such as Flair, Anderson, Piper, Raven, Savage, and Scott Hall in The Box, Jericho honed his skills that made him the great he is today.
If Jericho's "acting classes" worked for him, professional acting classes would seemingly be even more effective. Granted, some charisma and promo skills are going to come naturally to some more then others. But I don't see the negative, as this can only help with the little things,such as inflection, facial expressions, and delivery. I think this is a good call by Vince.