Oh hey, I never said anything about the responses here, did I?
So, Dream Land 2/3/Crystal Shards collectibles vs Amazing Mirror/Squeak Squad collectibles. Technically, Squeak Squad DID have both, with those seven star keys you needed to collect to enter the final two worlds, and this is pretty solid I'd say, maybe just make them needed for the secret final boss rather than the entirety of the final two worlds.
Most elements regarding bosses/enemies being too easy could be fixed with this emphasis on collecting upgrades. Both Amazing Mirror and Squeak Squad had a couple health upgrades already, just increase the number of possible upgrades, starting Kirby with a base health level quite low compared to most of the series, making collecting these upgrades that much more important for those who want the high number of hits available in most games. The base platforming challenges/enemy threat could also certainly be made more intense. These days most enemies attack so slowly/infrequently they pose no danger at all, speed them back up to Amazing Mirror levels and we've got something again!
While it may not be entirely true that Kirby isn't notably special at all, the fact of the matter is we do see other characters who can do the stuff he's capable of. Gooey, Keeby, Shadow Kirby, they can all copy abilities just like Kirby can, and of course all of these abilities ARE copied, single ability runs are typically possible in most games meaning the original owners of those abilities should also be able to handle these adventures. Kirby is the only one going out there to defeat these gods and monsters, but it does seem like many others COULD if they actually tried.
I don't have an issue with character voices whatsoever. Not as they currently sound/are used, anyway. If Kirby and co were going to get full speaking roles as I've suggested, some voice changes would probably be in order, but otherwise everything is fine. I could say the same about the lore and DLC, really. If anything in this deeper Kirby game I'd want them to EXPAND on the lore they've set up over the years, finally tie things together and explain just what the heck is going on. I do think keeping the Heroes In Another Dimension mode as DLC released practically a year later was kind of disappointing, Star Allies could've really used a mode like that at release, but otherwise the addition of the Dream Friends was a fantastic reason to keep coming back to the game.
As for the engine, there really isn't a reason to get rid of it. The controls are great and the number of copy abilities and Dream Friends they've added with it display a solid amount of potential for basically anything they may want to do. Nothing I've mentioned previously would warrant an engine shift, rather a shift in how the story and challenges are designed, which this engine seems perfectly capable of facilitating. Ultimately, I see nothing creating an entirely new engine would add unless they wanted to fundamentally change how Kirby games are played, like making a fully 3D game, but that's not what I'm suggesting and is a different discussion entirely.