There are two ways to accomplish this. The first is multiple tees. You can set par for a particular hole and then set tees such that par is attainable for the different skill levels.
The other option is to set different par designations.
I've seen both done and I think both are reasonable.
This ^^
In ball golf there will ALWAYS be multiple sets up tees that make par attainable for different skill levels. I too have seen this done well in disc golf. However, there are many courses that do not have room for multiple tees. Having both Pro/Adv level pars and Int/Rec level pars on the tee signs is very useful.
Using the "all 3s" method for scoring is very easy and a valid way to add scores. As previously stated par does not matter in competition.
I also agree with something else BradHarris posted regarding course design and reviews. My favorite disc golf holes are par 4s in the 475-600 range than absolutely cannot be reached from the tee. Holes that require and accurate drive to a landing area, then an accurate approach to the 10M circle. Holes like this really close the gap between accurate average distance throwers and guys who can just throw really far.
The OP mentions a specific course, which I have played numerous times. Hole 4 is 500+' uphill to in a wide open field. Literally no obstacles, no OB. While many will argue that this is a par 3, I would love to see what the SSA for this hole is for the last few tournament rounds. It is not and easy 3, and I would say it requires at least 550' of distance to have a putt from the circle.
Hole 5 is also 500+ feet (to the long basket), and while the tee shot is downhill across the same field as hole 4, the basket is up a hill across a tree/shrub lined creek. The basket is actually only about 2 ft below the tee pad. The creek is about 450' from the pad. Oh, and there is a walking trail along the backside of the basket (maybe 20' of clearance) that is also OB. In order to have a putt at this hole, you have to throw at least 500' from the pad, over a creek/trees, and short of an OB path. Again, this hole is not and easy 3, and any 2 should definitely be considered an Eagle.
to the OP, FWIW, my best round out there is a 58 casually, and a 62 in competition. Pro/Adv players will regularly shoot 48-50 in competition.
http://www.pdga.com/tournament_results/99878
That is a link to the results for a tournament held there in Feb. You can get an idea of how wide the scoring spread is between the top and bottom.