No, in the adventure mode, you get gems for every 100 points in your final score for that world, once you've completed it.
You can also get them from the reward boxes scattered throughout each world.
Getting perfect 20's on some games gives you a higher chance to unlock a bonus box, as that can open up extra paths.
You'll know if completing a game will unlock additional paths if it has a small click mixed into the normal two tone bling when stepping onto a game square.
Sometimes getting a perfect score in a game can also unlock the path to a bonus game, where you can wrack up allot of extra points, hence, a better chance for more gems when that world is completed.
Oh, and rarely, at random on some sidescrollers, you can find a teleporter that will take you to a special path above or below the normal game area that's got several gems to pick up.
Their are allot more ways to gain gems too, but that's later on.

If either of you want to be added to the Crazy Party Skype group, where you can get help easier, just give me your Skype name.

You can also get gems as gifts when playing in board mode as well, particularly in boards like the mischievous castle that have a lot of bonus gift squares.

I will say I wish there were both more things to unlock with gems and indeed more ways of getting them in single player, since once you've unlocked all the boards, hard mode and six party battle, the other unlocks cost several hundred gems each.

It'd be nice if prices for things were spread around a bit more evenly, also it'd be nice if you got more than one measily gem for each 100 points completing a zone, actually with the amount  gems you need for certain unlocks, and the fact that some things you can buy with  gems such as a pass to the unlock games world are rather expensive, imho it should be one gem per 40 points in single player, but hay, at least it gives something to work for, even if it'll take a lot of work, especially if your a more casual player.

Then again, I confess I've fallen off myself in the battle mode recently as I need to redesign some decs, so haven't played online battles for quite a while, and  believe online battling can earn you more gems than minigames.

didn't even know about the teleporters at all, so that might explain how rare they are. But also, I'm frankly not that good.

as for getting gems in multiplayer, you get them in reverse order to how you place overall, and I think also one for every 100 coins you have at the end of a party. for example by what I mean about reverse order, if there were 5 people playing together in an online multiplayer game, the person in last place would get 1 gem just for taking part, the person in fourth place would get 2 and the person in third place would get 3, with the guy who won getting 5, but I can't remember for certain if that is how it works. And then of course there is also what you get for getting more than 100 coins. Multiplayer is the best way to get gems because even if you get a low score, you'll at least get one. You can't say that for several of the single player modes. I rarely get gems from single player games except for the quiet woods board because I play long games and rock at the mini-games that that board gives you and also in the handful of worlds where I can find safe deposit boxes, I can get ahold of some sometimes, though even though I often finish worlds with high scores, I rarely break 100.

The deep water is my favorite. I can easily get over 200 points with that board. There are a few games which trip me up in the deep woods. The main one being that stupid hunting ants game. Ugh! Also, the bank can really screw you on that board if you're not careful.

Agreed about the coins. It does feel rather cheap that we have so many, and can't do a thing with them. I get that using gems as currency adds a certain difficulty factor, but what's the point of racking up coins exactly?

here are the games we've found that it can happen in so far.

Sometimes on the following minigames, teleporters will spawn that move you to a special path (or room, if it's a 2d game) with gems to collect!
In games with multiple levels, like underground or water, they can spawn at the bottom too.
If your playing online, their will be rubies their instead.

Wasps lake
Haunted forest
Windy peak
The fireclouds
jellyfish bay
jumping penguins
Boreal Forest
The Chasm's Cave
The flying boat
Underground facility
across the sewers.
The Hedgehogs path
Glacial Lake
The diamonds mine
The clocks of the village
The hidden palace

I love the flying boat, but it's a hair raiser!

I also just found out that you can get teleporters in 2D games as well, it takes you to a special room rather than another path.
I updated the list in post 14 with 3 more games, the last one is a 2D game.

Good to know, thanks!

Interesting list there defender.

I do remember finding a  somehwere out of the way in  wasps lake while playing an online game at one point, though I assumed that was more to do with random ruby placement than anything which might happen in single player mode.
I'll have to keep a watch for these teleporters in single player mode.

I've been thinking about this more, and I'm pretty sure I did encounter one on the hedgehog's path when I first started playing. At the time I was more concerned about racking up points, although I remember thinking, huh, that's odd, there shouldn't be a way to climb down in a pure sidescroller like this. I could kick myself now, though, because I haven't gotten it to show up there or anywhere else again. But at least I unlocked the castle board now, and it seems like you can get a decent amount of gems, because about halfway through the board there are a bunch of gift squares that will sometimes give you some. And since I usually get good scores on most of the games there, I end up with 300 coins or thereabouts.

well no one mentioned it yet, but an online micro game party (i go there and host them as juancholoco) can give you gems relatively quickly. You could play 5 of those in about 10 minutes.  Never ever encountered the portals though.
I am too bad at many of the mini games so I have not been even able to unlock much yet. It just irritates me some people go online and have this ridiculous amount of objects and gems which makes it just unfair for everyone else.