Lightheadness, vertigo, possible carotid bruit: should I be worried?

Yes get checked out. Symptomatic carotid artery disease places you in a higher risk category for a stroke, and indicates a need for a surgery called a carotid endarterectomy. This involves removal of the plaque buildup in the artery. In conjunction with medications, diet modification, and exercise, the procedure will lower your risk of cerebrovascular events.
Concerned. You should really get this checked out - you are at risk for TIA or stroke. Check with your primary and get a referral for carotid ultrasound to assess your carotids.