Comprehensive covers damage not caused by crashing, it does not cover damage caused by other drivers causing a crash. Comprehensive + uninsured motorist should cover you for all damage where you are not at fault in most states (California, Colorado, Georgia, Illinois, Louisiana, and Ohio don't allow uninsured motorist to cover damage from hit-and-run collisions). You'll need to ask your insurance company what the premium difference would be if you dropped collision and opted for uninsured motorist instead (you might have an uninsured motorist deductible waiver on your collision insurance, but that's not the same coverage).