All right: you, as Sorcerer GM, are not the judge of quality role-playing. You should instead consider yourself the voice of the group engagement. When someone does something that makes anyone or everyone react in an engaged, heightened way, it's worth a bonus die or two.

That's all. So you're not saying, “Gee, I'm stroking my chin and deciding whether you're ‘acting’ well enough.” Instead, you're saying, “Wow! Cool!” or seeing someone else say that (or nod, or smile, or grunt, whatever) and then remembering that it's worth a bonus die. The rule is based on acknowledging that something said or done by someone else was fun for you.

Therefore, bonus dice are not incentive. The net effect may be to see more of it, but that is not the point. The point is to celebrate the medium you’re utilizing together.

That’s why bonus dice in Sorcerer are not about long, drawn-out, extravagant descriptions of actions. They usually get applied because of the quality of a given stated action, which includes its timing. Here's an analogy from film: in the first Indiana Jones movie, a guy comes running at Indy to kill him with a sword, doing all sorts of crazy whirly sword-moves. Indy grimaces in a kind of «oh come on» way, pulls his gun, and shoots him. My point is that in role-playing, an equivalent reaction and stated action typically make at least one other person at the table cry out or smile-and-nod or otherwise react in a positive way, because their fun just increased. That's what you, as GM, are keeping an eye out for, with yourself as a possible reactor as well.