Keep in mind though that the Minimunks movie was made quite a few years before these movies... Ross isn't quite looking so youthful these days either; matter of fact, in the most recent pictures I've seen of him, he's completely gray now... BUT, you know, that doesn't mean that he couldn't have coloring, or wear a wig and such to play Dave... especially since his father's passing, he IS Dave. Much like how 60s Dave (from The Alvin Show) looked like Ross Sr, 80s/90s Dave bears resemblance to Ross Jr.
But, you know what's odd? Even if Ross and Janice still did the voices, it wouldn't sound exactly the same, because they actually haven't been recently... in some of the more recent songs and such, Alvin's sounding a lot more like Simon, and Theodore is sounding a lot more like Alvin... and I don't even know what was up with Brittany's voice in the Wolfman movie. I know they actually still do the voices in the old-fashioned way of recording them at half-speed, on analog tape, then speeding it up (people like to say otherwise, but Ross and Janice have both confirmed this in recent interviews), but maybe they're not being sped up to a certain speed like they usually do, I don't know.
But, you know what's odd? Even if Ross and Janice still did the voices, it wouldn't sound exactly the same, because they actually haven't been recently... in some of the more recent songs and such, Alvin's sounding a lot more like Simon, and Theodore is sounding a lot more like Alvin... and I don't even know what was up with Brittany's voice in the Wolfman movie. I know they actually still do the voices in the old-fashioned way of recording them at half-speed, on analog tape, then speeding it up (people like to say otherwise, but Ross and Janice have both confirmed this in recent interviews), but maybe they're not being sped up to a certain speed like they usually do, I don't know.