Cruor covers the cost of Rubicund should you use them, as NMs normally give 15k+ cruor. Cruor exchange rate for cruor>gil is 2.595 gil for 1 cruor. Doing the math you can see that 15k cruor is roughly 40k Gil. That means in a single kill you make back most of a stack of Rubicund Cells in worth. Now when you factor in the fact your using 18 per run of 6 kills, at 50k a stack, that becomes 75k total, and in 2 kills you make back the gil. The other 4 kills are pure profit, with or without plates and without counting in other drops that you NPC or sell on the Auction House. So really plates have nothing to do with making up the cost of Rubicund in my opinion.
As forI think good items would still be highly valued if they are good gear, such as these feet. If they were not good, why would people bother in the 1st place? I don't know, maybe I just misunderstood what you meant here but reading this made no sense at all to me. Its not like you can sell the boots, and its not like their value drops if you get them easier, they are still just as good either way, so just as valuable.Lamorak has a high-value rare, which is both worth spamming him for and would not be nearly as high-value (just like plates, go figure!) were it not as rare.
As for being limited on stones, this is why dust exists, and if you go back to the math I gave before, 4 kills were pure profit remember? Now those last 4 are roughly 160k when the cruor is converted into gil, now, dusts are 20~25k each, so even at 6 kills buying 1 dust per kill for the 6 stones you end up with paying at most about 150k. This leaves 10k profit before item drops. So really limited stones, rubicund, warp costs, and all that, are covered by ones cruor gain each fight, leaving drops such as plates to be pure profit. This is why I said people do those runs for money as well, not to mention Kaggen, Akvan, and Pil have seemingly higher drop rates on singles than Zilart does on pouches. I myself goto these parties for money because I know for a fact they are profitable to me no matter what I walk away with.