Under normal circumstances, it'd be pretty annoying if the translators started changing levels and rosters and stuff for no reasons. But it'd be pretty awesome if they raised some levels here and there.
But really, the HGSS 2.0 is not a bad idea at all. I almost wish they didn't add all the Crystal stuff in HGSS so it would've given them an excuse to make a third version other than to increase levels and change Pokemon. I'd even go through the trouble of making a rom hack if I could, if only I knew how to hack a game, much less a DS game.
I agree with you that HGSS could have been better in the levels respect, and that a third version would have been a good idea. For example, what would fans do if GameFreak remade Ruby and Sapphire but not the clearly much more sufficient Emerald, even if they included aspects of the third game? If those hypothetical leader teams were the same as the notably weaker R/S teams, GameFreak would not be able to stand; its legs would be ripped off.
Clearly a shake up in Pokemon and levels should occur in a remake.
However, despite me being upset with the initial teams, I find that the rematch teams are mostly sufficient. Of course, no one should have to go through the breeze of fighting a Level 48 Pelipper (Falkner) after beating a Level 60 Pidgeot (Green), but given that that said Pelipper has Tailwind, a good strategic team move, GameFreak did not completely sit down and do nothing.
In my opinion, GameFreak felt no need to change the initial gym rosters because it is after all trying to capture the classic feel (though Green has never before owned a Machamp, which makes it understandable to be upset that Bugsy did not even teach his cocoons Bug Bite, let alone evolve them). However, they should have at least made the rematch levels on par with at least Blaine's team (level 54-62). Still, I cannot make a clear judgment of the leaders until I actually play the game.
Edit: Would it be worth spending a year on a Crystal remake to correct the levels?