Ultimately, dividing total GRC magnitude/daily coins evenly among each whitelisted project is the primary issue. If the PoR mechanism somehow was able to reward people purely based on how much work they were doing (IE: two identical computers maxing out their CPU/GPU at 100% for a full 24 hours earn the exact same amount of credits regardless of which projects they were working on respectively) we could simply whitelist projects based on how valuable they are to science and make this process so much simpler.

Regarding gaming of the GRC reward system, it would basically work like this: if we had 10 projects that only divided out workunits once per week for a short time, I could simply dump my current projects and sign myself up for all 10 of those projects. Since most of these projects simply put their workunits in a big bucket and crunchers take them "first come, first serve," I would effectively be in 10 different "lottery" systems. I might only be crunching 25% of the time, but there's a pretty good chance that I could achieve a magnitude equal to someone crunching 24-7 for SETI, PrimeGrid, or any other project that requires 24-7 crunching to compete.

In a situation like that, you wouldn't even necessarily need a good crunching computer. Load up a BOINC client on a dozen old laptops to maximize your chances of getting workunits. Set each client to accept as many WUs as possible, and you've basically built yourself a Gridcoin mining farm that could get 1,000+ Magnitude on a cumulative computing power less than a single GTX 1070 and maybe an average of 200 watts electricy.