This happens in my games as well. Often though after I apply the BBEG personality/style to the idea it might not work or there might be a big twist to it. If it fits then use it, as long as you don't have to retro anything the players know about. Sometimes the players brilliant ideas are perfect but the villian isn't and he missed that chance to be perfect. I like the villians with flaws and having commited to something else.
Also even if the player is wrong often these brilliant deductions can be used to show the players why the BBEG is acting a certain way. If the players question why he didn't follow the perfect plan it may give them insight into the BBEG plans/motivations, that can be a reward for thinking up something cool.
later
Also even if the player is wrong often these brilliant deductions can be used to show the players why the BBEG is acting a certain way. If the players question why he didn't follow the perfect plan it may give them insight into the BBEG plans/motivations, that can be a reward for thinking up something cool.
later