I honestly feel you should add a few more emerald tokens in stages. At least 1 or 2 per stage, unless it's a boss or transitional stage. ...or non-traditional stages, although I still feel like there should be a couple of those with tokens. Hide some of them well, give others a nice challenge, but don't make them really hard to find without using the devmode map and/or noclip. Oh yeah, and make MOST of them accessible with sonic, obviously. SRB2 still has some non-sonic accessible tokens, so it's already to leave a COUPLE of them, but not too many. But, you have to at least give most of them a challenge, such as navigating to them, or generally looking hard for them, and make sure the player has to at least put in SOME effort into looking for most of them.
so basically do a good job at hiding emerald tokens.