With MR connections, there is also the possibility that you get re-routed and get to your destination earlier - same with voluntary bumps, in which you usually get your original mileage credit plus a voucher.

I have had pretty good luck with rebooks not delaying me too much. I agree with the suggestion about checking out alternative flights ahead of time. Do it from each point on your run. It will help you to find out if there are many options or few in each case.