The Silver lounge sucks, don't go there. It's NOT worth $82.
The Gold lounge is definitely worth the extra $14. I found the Platinum lounge to be on par with the Gold; not worth the extra IMO.
Al Mourjan is definitely the better one of the lot.
It's up to you how much money you're willing to part with. IMO it would be between Gold and AM, and whether you think the extra $42 for a nicer lounge is worth it to you for all those hours. (They both have showers and vegetarian food options, so if you don't care about the nice factor then the Gold would be the winner IMO)