I would argue that at least some of the time-delimited exercises do stimulate creativity.

As I like to twist the Toastmasters credo, "Learning to speak within the allotted time is not just a skill, it's a way to force your synapses into firing differently when you have 1 minute left to deliver 5 minutes' worth of speech."

But I see your point.

Some of my favorite exercises come from Natalie Goldberg and Julia Cameron, both writers who teach creativity. Specifically, I"m thinking of two: Julia's Morning Pages (or "AM PP", for the lazy of hand), which is three pages of mental vomiting on the page, first thing in the morning, only stopping allowed for punctuation; and Natalie's First Thoughts, which is a timed exercise. You pick the time--I like "sprints" or "etudes", but again, about blasting through blocks. And crazy stuff comes out, trust me.

Both of these are similar in that they remove (or try to) the judging, telling one's inner critic to STFU. In my own experience, this gets me the most bang-per-buck, creatively speaking. An exercise like writing without "e" would just make me nuts.

It occurs to me that a lot of games are predicated on this construct of taking something away or imposing artificial constraints: you can't say a particular word (or use any words), or you have to use the last letter of the last word to start the new one, etc. Great improvisers are crazy-creative, for sure.

Personally, I've always hated party games, and even improv, except as a rehearsal/creativity tool. I'm very competitive, but have a deathly fear of doing something wrong, so they make me panicky.

But YMMV and chacun a son gout and sh*t.