Guess it all depends on how you work it. I'm by no means the best producer around, but I've been making beats for about 6 years without the aid of an MPC, and I've made some pretty ill ish at times. I recently got a MPD (sort of my intermediary to investing in an MPC), and it definitely can give you a bit more flexibility and on-the-fly creativity with samples, but you can make something ridiculous without it.