In my opinion it is worth it.
As @Marcin said, Android is more of a open platform then iPhone. And it's easier for developers to start with developing applications and putting them on the market.
But it means the market is populated with a lot of crap applications. And then, there are really shiny jewels too. They get good scores, are blogged/twitted about and are popular.
So, in my opinion, if you got an idea for a good game, go for it. If you put it on the market though, consider putting (at least a 'lite' version) in the free area (people in some countries are unable to even access the paid applications market).
the below part is completly my own opinion and you can simply skip it
There are some 'cool' games on mobile platforms that I love to play. As for me, there are few important things to watch for when developing such a game, that aren't this important in more 'traditional' gaming, on a console or PC:
- it should be easy(fast!) to start and stop. If I play it at a bus, it could be just 1 stop. If it starts right away and then doesn't take 5 minutes to stop it, it's a +
- one more thing about rapid start/stop. If I quit the game, then come back, give me a chance to continue where I stopped. No need to ask if I wanna save/load last game. Make it default, I can always start a new game if I want, can I?
- controls - even that accelerometer-using games are fun at times, try to play it in a crowded place. like a bus. Touchscreen elements should be large enough so even the thick-fingers can use it. If they are - it's a +
- for long time I was trying to realise why playing Bejeweled, or Puzzle Quest, was fun and enjoying, while many of their clones were simply irrytating. The diffrence was a tiny piece of user interface - in Bejeweled the pieces you got are both diffrent colors and shapes. They are much easier to "operate" (in a Bejeweled way) then, say, screen full of diffrent color triangles. If you make a game like this, make the diffrent pieces differ in many ways, not just one (diffrent shapes with same colors would suck even more; red triangles, yellow circles, blue squares and black skulls is a way to go - in my opinion)
- it's a mobile device, connected to either WIFI or 3G network, you can use the internet to at least show/save highscores. But - remember - sometimes there's no network, we're in a diffrent country with roaming turned off or on the bottom of the ocean. Make the game work even there