My wife and I have been doing the Rubicon JJ, off-and-on, for over 30 years. The first one we attended was in 62. I would recommend the trip for a 'first-timer', as a way of becoming confident in what your vehicle can do, and having readily-available help and advise. The Rubicon trip even has helicopter service, medical help, and mechanics. The attendees are typically (at the Rubicon) made up of about 75 percent 'repeats', and about 25 percent 'newcomers'. So, there is a lot of 'family' feeling... We have many friends there, that we have known many years, and see only once per year on the trip. Having been over the trail numerous times, I never go anymore for the trail 'experience'. To me, the trip is for the party, being a 4-day adult party. (The Jeepers Jamboree, 4-day Rubicon trip, is always the last full weekend of July. Children under 14 (?) are excluded. As I mentioned, this is an adult party.) Any vehicle that can fit the trail is welcome, and indeed, almost any vehicle will be seen. Jeeps are predominate, though, the older-the better. Quite a few LC's, occasional Land Rovers, Patrols, early Broncos, Scouts, Jeepsters, mini-pickups, Samaris, Cherokees, GCs, etc. One of my friends even took a FS Blazer through, one year (did lots of damage). Some parts of the trail are quite tight, and smaller vehicles fit better. Bigger vehicles tend to have problems, and get lots of damage. Stockers can do the trip, perhaps taking a short bypass in at least one area. The majority of the trail has no bypasses. Rock-crawlers, and low gears are a plus, but are not absolutely necessary, unless you want to spend some time playing in the little sluice. There are always a few roll-overs, caused by stupidity and/or alcohol. Or, in the case of one group that comes, they do the roll-overs just for 'fun'. The food is great, and the Sierra scenery is wonderful. Some years we've had rain, or even snow, but usually the weather is great, no matter what. Not to be confused with the Jeepers Jamboree, is the Jeep Jamboree, and, is always the following weekend. The format is the same, except it is a 3-day trip, and it is limited to Jeeps only.
As an aside, I will mention that there is currently a lawsuit against the JJ, from a guy that walked into a (running) helicopter tail-rotor. For some reason, the damn-fool isn't greatful enough that he is still alive, and he and his lawyer are trying to fix the blame on someone else. This person is a member of the press, from Germany (I believe), and had been on the JJ several times previous to the accident. He knew where he was, on the helicopter pad, and apparently, he is not able to accept responsibility for his screw-up. I hope that he and his lawyer are not successful, and screw-up the trip for all of the rest of us.