Biggest advantage has been access to the lounges. Nice to be able to get back to the hotel and have a few drinks and food after a day of sightseeing. Breakfast in the restaurant (7 days a week outside US & Canada) if there is no lounge is also good. Free WIFI is worthwhile when travelling overseas in particular. Late check out, we have asked on the morning of check out and it has not been a problem. In Rio we were allowed a late check out of 6pm! The bonus point difference from 20% to 25% isn't much. We haven't received many room upgrades as such, more like the room is in a good location (higher floor with a view & quiet). That is fine with me as I don't expect upgrades, but if they come along I won't turn it down!
Here are all the details for you to read:
There is a limited time offer to gold and above for Marriott cheques for 135,000 points for $1000. This is a very good deal and the cheques are disappearing in Jan., 2013. If you use points for room stays, this would be a good alternative because the nights would count using the cheques. Also, if you stay at hotels that give you 10 points per dollar spent, that would bring the point value back to 125,000 points, and then the 25% bonus would give you another 2500 points bringing it back to 122,500 points. They aren't secure and no change can be given to the $50 cheques, however. I've never had a problem with restrictions on special rates like Sr.
There are the gift cards, also, that offer 10 points for every dollar up to $2000, good until the end of the year.
The gift cards and cheques might not have a good exchange rate overseas, though.