Just a quick thought here.
One of the things that I find really compelling about princec's Titan Attacks is the power-ups. It adds a bit of strategy to it - should I go for the speed upgrades early to try and clear the challenge modes? How low should I let my shield level go ('cause it gets much more expensive to 'maintain' it at a high level). Etc.
I was just checking out the Chuzzle and it's two cl*nes - Gem Shop and Fairies. Of the 3, Gem Shop held my interest the longest, despite having the weakest graphics. The reason? Again, it had an upgrade system which in turn required making some decisions which, on the surface are pretty simple, but actually seem to affect things a fair bit (save for the expensive jewelry? But lots of customer happiness treats? etc.)
I'm not aware of any other casual games doing this, but I like it and will try to incorporate the mechanic in one way or another in my next game...
I, too, am fond of the upgrade mechanic. It's typically very addictive and serves to carefully progress the game in a far more appealing way than built-in linear progression allows. I think of the reasons it works so well is that it creates a meta-environment in the game -- a place where the player is directly responsible for shaping the outcome in a creative way.
Any time a player has the ability to choose, accumulate, and organize additional gameplay elements -- at their own initiative -- the game opens up a whole new world in which the game they're playing is no longer constrained by the progress you've organized for them, but they can now embark on a trek of their own, and in a wholy personal way. They're now experiencing two adventures: The unknown of the game they're playing, and a whole new game (organization and assimilation of earned resources) that they are responsible for creating, real time.
This meta-game adds volumes to the value of many games, and expands the game beyond the arbitrary limits set by another person (the game designer) to an individual experience in which each session is formed and owned by the player himself. Any time you can involve the player to create their own meta-game is a good thing, because it means they are in control, and that's the primary reason players play games -- to exert control.
I had every intention of adding this mechanic to my current title, but as time has obviously gotten the best of me, I am only left with an idea for a sequel. If I didn't feel so pressured to get this game out, I would impliment this upgrade mechanic in a heartbeat, because I feel it adds so much to the game. (That also tells you what kind of hurry I'm in!) Let's just hope I get there before any cloners do!
It might only really appeal to the "optimisation" types though. The fact that it feels nice might just be that its a clearly visual effect of doing well.
I'm wondering if you just had some items that went "ping" nicely but otherwise did nothing you'd feel the same way. Or at least the average casual gamer who really hasnt gotten a hold of the whole "power up" mentality.
I think tiny snippets of positive feedback has far more going for it than meta-optimisation strategies as an incentive.
For instance, which of the 3 games tended to offer you more in the way of positive "youre doing well" reinforcement? Which did a nice "ping" more often?
I did a quick stufy of the zuma clones and realised that Zuma was far and away the best as rewarding the player for playing with nothing in particular, but lots of little bits that altogether made it a better experience.
I'll have a look at the 3 games you mention and see if I'm right.
Another example is in diner-dash vs that one with the cowgirl in the bar (sorry forgot the name, wendys something?). The people who get served quickly and well in diner dash have a really pleasing "V sign" graphic, which is often used in japanese culture for happiness in pictures. I think that kind of thing reinforces my pleasure in diner dash over wendies, even though its roughly equivalent in mechanic.
Dont pay too much attention to optimisation based efforts as thats pandering to the hardcore when you might just be as well making a nice sprinkly graphic and a ping sound!