I get where you're coming from OP. The problem isn't the ability to grind missions being removed, the problem is only a handful of missions give worthwhile rewards. Simple solution for R*: re-evaluate the difficulty of certain missions (EX: Last night Martin's "kill the lawyer" assassination mission was buffed to a 9k payout. This mission is vastly easier than VD in theory yet now VD has a 3k payout...wtf...Also, all Simeon missions are way too "difficult" for their crap payouts) and re-evaluate rewards.
In fact, the best solution to keep random jobs worthwhile is to SCALE REWARDS. At rank 1-10 you should be getting 1-2k per job. At 11-20 you should get upwards of 3k, 21-40 should give upwards of 7k per job, 41-75 should give upwards of 10k, 75+ should give 10-25k. This isn't the job rank, this is your rank. Rewards should scale...that way Pier Pressure or any Simeon mission may actually be worth doing for the time investment.
This is, of course, only referring to jobs. The actual multiplayer competitive stuff is actually pretty well balanced in it's reward structure. Not everyone gets into PvP as much (me included), and I only do these things as a means to an end (ex: racing for car mods). I get more enjoyment of out of co-operative PvE stuff...it's included in the game...the rewards are just a mess atm.