If you were attempting to find casual gaming gold, you might well think about trying to create a game at the midpoint of Plants Vs. Zombies and Diner Dash. That's pretty much what Black Market Games (created by a group formerly from Dark Water Games, they of Dogfighter) have done, with Dead Hungry Diner. A game in which two canny orphan twins realise the best way to thwart the zombie apocalypse is to feed them. In a restaurant. In a graveyard. You can check out the first eleven levels to see if that works for you via the demo.
After zombies come vampires, angry zombies, and giant hulking Frankenstein-made monsters. And along the way you can purchase more magical items, in a very PvZ way, to manage the huge numbers of customers coming your way - perhaps a raincheck ticket, or giving them a little more patience with their wait.
I've never much enjoyed Diner Dash, firstly because it's so humourless, and secondly because, screw the customers! Here there's a bit more logic. If we don't serve these monsters in time, they'll leave and eat the villagers. It makes some sense, in a world of nonsense.
It gets ever more complicated, with werewolves appearing, and refusing to be sat near vampires, demon hunters cursing your monstrous customers, and so on. And the demo is extremely well paced, introducing new features at just the right rate to ensure you feel on top of things, but still with that sense of frantic rush, and eventual relief of completion. I've only played the first ten or so levels, but this really does seem to have the polish of a PopCap game, which is high praise indeed.
You can get the demo directly from here.