There really is no right or wrong answer. The bottom line pretty much seems to be the individual's tolerance to standing in lines. I really don't see it as much of a time-saver. On incoming flights, by the time we get through the lines, we usually still have to wait for our luggage to come out through the carousel anyway. Plus, the shuttle bus will wait for the non-Club Mobay people before departing. On outgoing flights, Couples gets you there early enough that there is still plenty of time to shop and eat after customs.
Personally, we like to use our time shopping at the airport rather than waste that time at the resort, plus it has never taken us more than an hour to get through the lines, so the Club Mobay price isn't worth it for us. Of course, I've never understood the people that pay hundreds of dollars for Timair just to get a couple extra hours at the resort when you could stay a whole extra night for that price. To each their own.