Spent a little over an hour de-tarring my blizzard white Prius today. One benefit of having a grey or dark colored car. After an hour all I could think about was Mr. Miyagi saying wax on, wax off. The worst area was the two front doors BTW. I spent more time on each front door than the rest of panels on the car combined. I started with front left fender and worked my way to the back then worked my way up the right side, finishing with the front end. Hint if you decide to de-tar the car finish, start on the two front doors first. After already spending 40-45 minutes working on the car the front passenger door was a real pain literally. In other words do the two front doors first they take the longest and require the most elbow grease to clean the tar spots off of.
I don't have mud guards and I used a bug and tar remover I had laying around called Trax that I bought at Advance Auto. It wasn't that there was a lot tar, it was that it covered so much area with these tiny little dots all over the side of the car. Probably from cold patch asphalt they use to temporarily fill pot holes. It wasn't that it was hard to get off but it was everywhere. You look at the car from five feet away you would see the tar streaks on the rockers and a few small marks on the door. It wasn't until I got right up on top of the door to clean it that I realized this cleaning job was going to take awhile. All together the front fenders, quarter panels, tail gate & rear bumper, hood, and front bumper took less than ten minutes to clean. I might have five minutes into each front fender. For the rocker area that was where the most was yet it cleaned up pretty easy. The doors, it was the shear area and coverage of these pin prick dots on them. I'd do a 3"X3" area and move on. Look how many square inches of metal are on the door of Prius.
I bought some polymer sealant called "Rejex" - I have a White BP so I have the same issues as you. Now all those tar spots come off with a moistened terry-cloth and some slight rubbing. So far 1000 miles & 1 month, the sealant / coating is still there (car still feels slick when running a finger over it).