Mega voices add a lot of legitimacy to the styles and definitely make a noiceable improvement. Unfortunately Megavoices are not designed to be played live and a lot of people feel misled when they find out megavoices are for styles and midi sequences only.

I think for arranger keyboards the Megavoices are not at all over-hyped and really help get away from the canned MIDI sound.

Megavoices are also a wonderful asset for anyone who is up for making their own styles. I'm sure it would take a lot of work to get incredible results; but the capability is definitely there.