Badger, as a once-expected-to-be EC 2015 participant I agree with your first suggestion (and I'm sure there will be a lot more to come) to require some sort of evidence-based demonstration of skill and/or experience. And, this is coming from someone whose efforts to get into an EC event could only be hampered by more hoops to jump through.
I agonized over my decision to withdraw one day before the deadline because I did not have my boat where I thought it should be in consideration of the advice I got from veteran Tribers AND I felt really uneasy about the likelihood that I would not have the time left over to get the needed experience with my newly arranged rig, such as what you'd get by doing something similar to a derby.
As far as a buddy system is concerned, its a good thought but I, for one, would not want to be a drag on another sailor. In fact, it took all available restraint to refrain from begging myself into someoelse's boat since having no EC-like experience, I would never have wanted to put myself or any generous shipmate in a position where I needed to tap out for any reason or my presence took away from their adventure and enjoyment.
I won't go so far, yet, to say that the casualties experienced during this year's event will ultimately take anything away from the event to any large degree, since I was neither in their shoes nor alongside them to witness the specifics... weird things do happen on the water that would challenge even the very best of us even if within a few dozen yards form one another. I won't get into the excuse-making bidness for anyone but rogue waves, whirlpools, submerged objects, sand bars, crab traps and congested traffic readily comes to mind that could easily affect one boat but not the other.
In fact, its entirely possible that an even bigger, fresh crop of "natural born risk-takers" attempt to participate next year - making the inspection and 'qualification' review process for events to come even more important.
I respect the USCG tremendously, but would balk at assigning them responsibility for calling the 'gatherings' on account of safety issues of one sort or another - it would be too easy to pay your fees and then have it cancelled on account of some perceived unnecessary risk. If the gatherings were all that safe there would be no "Challenge" in the "Everglades Challenge".
There's going to be a lot of soul-searching and hard decisions being made, but I fully expect it to be a better event as a result.