Fun list. I haven't spent a whole lot of time with C3 yet, but I like your ideas to push the limits. I especially like the conditionals idea, it makes me wonder how deluxe a game could be made with one event. Anyways in the spirit of the topic here are a few more ideas:
8. Utilize behavior's as much as possible instead of events. A behavior won't always fit with what you want to do but it sure is nice when it does or even is just close enough.
9. Make a simple scripting language to control your game. Admittedly it may be pretty tricky to cram that in 25 or 40 events but if successful you'd be able to have a lot more logic. Being able to type multi line text for text properties in c3 is useful for this.
I'm drawing a blank for any other general ideas, no doubt there others.