One friend of mine said he saved $6,000 on his 3500 by not getting 4WD. He said that was good because that was the same cost of getting a good winch system after he got stuck several times.
If all you are going to do is stay in RV parks and avoid situations where you might need 4WD good luck to you. However, if you look around at new and used 3/4-1 ton diesels you will find it difficult to find one without 4WD.
I have used my 4WD in RV parks when I was on a rather steep incline when I hit gravel. I would have stalled or slipped backwards on the gravel.
Still I camp on gun ranges since we do Cowboy Action Shooting. 4WD won't get you out of every situation, but when it doesn't just remember with 2WD you would not have moved at all.