Christian, like I said it is possible to do it but just be careful when driving. I take it that you have never been to Cuba and that, this is your first time. Cuba is not Mexico or Argentina, just keep that in mind. I have been to Havana, Varadero(resort only 3 days each time), Santiago, Santa Clara & Trinidad. Yes I agree with you, being stuck in a resort sucks.
Just enjoy and have fun, I have been going to Cuba for over 12 years and I never had a problem, but I also never drive as I don't see the need to do it as they have a great bus system.
So have fun and enjoy, make sure you have a good insurance plan with you.