I have towed CRVs for almost 50,000 miles. I have a Roadmaster Guardian rock guard that sits in my garage. I did use it for trip to Alaska but have not put in on since. I really have not suffered any damage and I do not like the hassle of having to store it (although not a big deal since I usually just stuck in under the coach on my Alaska trip.). I guess I find the simpler I keep things the better I like it. I use a Roadmaster Stowmaster 5000 that was my dad's before me. While it is old fashioned to have the tow bar on the car, I can hook up and unhook faster than my brother with his Blue Ox on his mh. I would not bother with a shield even when I make another trip to Alaska.
You pick up dirt with or without the shield. While it probably helps a little, these shields are, in my opinion, vastly overrated. I do have mud flaps on the mh that are set as close to rear tires as possible and extend to within an inch or so of the ground.