If you need sprint work, then sprint, and do it early in the ride so you can more easily induce the proper training stress.

It depends on what "in good shape" means. If that means you have an FTP of 4.5 W/kg, then that's different than saying you can complete a century. Go over to the 33 (racing forum) and lurk in the training update thread to see what people are doing. Everyone is different. You need to learn your race limiters and mitigate those while developing your strengths (note that strengths and limiters might not be related to fitness, but strategy, bike handling, gear selection, etc.).