A four-inch lift would be pretty radical. You'd alter the angles of the axles and wheels so much that the life of CV joints would be reduced. That might change the effectiveness of the vehicle's stability control, too. I lifted my TDI Beetle by two inches, years ago, and that was a significant change that bro
ught no ill effects during the next 50K miles I owned the car. If I ever feel like replacing or upgrading shocks, I'd do a one-inch lift on my C-Max just for a little curb and pothole protection.
This question has been asked here before, but no one has reported doing a lift. I have seen one spacer kits out of Russia listed on ebay, so maybe that's an option. I've always assumed that the suspension parts are interchangeable with Ford Focus models, but I haven't confirmed that. Nobody seems to modify C-Maxes, and the online community is thin, so you're on your own, Mi Amigo.