Don't repeat unless you don't believe the vitals for whatever reason. Yeah don't repeat them unless you want to waste time. Do a spinal exam for everyone if you can though, and make sure to ask before you put your hands on them.
Yeah but the fact is, "why bother?" You don't need to repeat any vitals to pass the exam and there is so much else you should really be covering in the encounter. Sure it only takes a minute, but why not spend that time counseling the patient or explaining their condition?