So obviously gems were supposed to give you an extra life. That's what the text in Rabbit in Training says, and that's what they did in 0.98k when you got 100 gems. 100 was also the number of gems to make the gem counter disappear, so that was presumably the highest possible reward. But was it the only reward?

The thing is, the manual makes gems out to be a big deal. Page 14:

Fortunately, each level is also chock full of weapons, ammo, gems, power-ups and other goodies to help you in your quest.

Page 29 (talking about the Continue screen):

You will start at the beginning of the level you left off in , but all your points, gems, powerups and weapons will be taken away.

Page 34:

Gems are what make the world go round. Collect gems to earn end of level bonuses and extra lives.

It's unclear whether this means [[end of level bonuses] and [extra lives]], or whether it means [end of level [bonuses and extra lives]]. Either way, it explains why gems are tallied at the end of the level, even though in 0.98k the extra life is granted right away. But what might those "bonuses" have been?

My speculation:

The tally makes me think of score multipliers the way you'd get in Sonic games. But also, since JCS treats "secret levels" and "bonus levels" separately, and the 3D stage assets turned out to be intended for episode transitions, maybe at some point the gem tally would take you to a separate bonus stage filled with goodies, like the signposts in Sonic 3.* And then, that was either replaced with the bonus room warps within levels themselves, or they both existed and the one that was more work was scrapped for being redundant.

* Some bits in Jazz 2, like the poles you spin around or the characters having different moves when pressing jump twice, have always made me wonder if where JJ1 took inspiration from Sonic 2, JJ2 took things from Sonic 3 & Knuckles. After all, Jazz 1 was released the same year as S3 and S&K and actually predates the latter by some months, and during Jazz 2's development there weren't really any "mainline" Sonic games, while a lot of platformers moved to 3D instead. Would be cool if we could get CliffyB to do an interview about it or something. Or maybe it's in his book? I haven't had the chance to read it yet.

But what might those "bonuses" have been?

Points?