Just for my own edification, I whipped up some napkin math. Using a type 9 with 500 cargo, hauling 50 free merits every half hour, and buying the 450 (and then 500) merits goods, then hauling back a 1400 cr / t cargo (not all too difficult, i found one on my first try) and factoring in a 16-17 minute round trip (reasonable from my experience) you wind up with an 8.1 million deficit per trip. Maintaining rank is 5334 merits, but we'll assume you just need 5k, because what's a little bit of combat anyway? So that means 5 round trips at 16 minutes each, 80 minutes, or 1.33 hours. (BTW, merits still scale with level- it's not 100k to fast track your current order, it's still 10k credits to fast track 1 commodity, so half a mil to fast track 50 commodities).
Anyway, what that gives is a net deficit of 40.5 million credits, and then a gain of 50 mil at the end of the week, for a net profit of 9.5 million. (The 1400 cr/t profit was rolled into the cycle cost) for a time investment of 1.333 hours, or just over 7.14 million per hour. The profit goes up if you take a bit longer of a route or don't grind it all at once- in my model, every other trip is buying 1 set of commodities rather than waiting 14 minutes for it to be free (for a net gain of a mere 2.5 million credits, but that bumps it up to 9 million per hour, PROVIDING you do things in the mean time- you'd have to go out and do some BH'ing in the system for 14 minutes or so every other time).
Point is, this is a bunch of work for next to no real reward compared to what is normally easily achievable, and the only real benefit to having rating 5 is the rating 5 specific bonus (since rating 4 doesn't give anything either).
That's really the lynchpin of whether you should maintain rating 5 or not, not the profit. (oh, and i guess RP or whatever too, if you're invested in the storyline).
(anyway, the worked-out profit per hour is just my main reason why the 'merit earned' decay is the proper model).
The big questionis : do I play this game to become a Math teacher ( I could if I wanted) or do I play it because I want to relax and chat with mates and have fun ?
Guess !
Yes you win the 64 000 credit prize !
I want to have fun.
PP is not engaging = no fun
Simple
Cheers Cmdr's