I prefer the second option I gave--making it easy to improvise cool stuff--because it encourages players to actually do that stuff, which I want to have happen. Unfortunately, I have this automatic processing that happens when someone suggests such an action, that unconsciously evaluates it against all class abilities and such for balance, as well as analyzes whether I want this happening all the time (precedent), which generally means my first response is to say you can't do that.
To counter this tendency which is at odds with my goals, I've explained the situation to the players, and encouraged them in those situations to just say, "Are you sure, DM?" (as in, "Are you sure you don't want to allow this?") as the reminder to me that I want to allow that stuff, and I can always disallow it next time if it is a problem.