Don't use MK. If you pick up MK to counter a few bad matchups, then you're going to realize how much easier it is to win using him instead of Lucario, and then you'll eventually just drop Lucario. You're only going to become another MK clone.
I think a part about the drive for competitive smash (other than the money, friends, fun) is getting recognized as a good player. Everytime you did well at a tournament you would come back and tell me you were pumped about getting your vids online to get yourself known as a decent Lucario player. If you pick up MK then you're just going to get recognized as someone who wants to take the easy way out.
Sure, you may use the argument "play to win", but if you're going to have that mindset then people start to lose respect for you as a smasher. Now I know you should always have the mindset "play to win", and that's fine, but I know I have lost some respect for Fenix for counterpicking MK against me.
If you want to beat Falcos then get better with Pikachu, or Ice Climbers or something. Those two characters do well against Falco but they're not going to tempt you to switch mains entirely.
*sits and waits to get chewed out*