djb, I came to the same conclusion about the standard Marathon tires. I think they are a good compromise between weight and durability. I ordered two sets of regular Marathon tires online and hung them up until we were ready to start our tour. When I went to install them, I realized they sent Marathon Plus tires by mistake. Luckily, my wife also needed tires on her utility bike and one set went on it. I sold the other set on Craig's List. They were like anchors. I had them too long to return them to the shop.
We started serious touring on 28mm Continental Ultra Gatorskins which were great tires. We used them to ride across the U.S. We did have 13 punctures on that ride, about a quarter of them from Goatheads. They were the lightest and fastest tires we've used, but not very puncture resistant. We upped it to 32 mm Ultra Gaterskins, and rode them for several tours. On one of our last tours on those tires I had 5 punctures, four during the last 4-5 miles of a 1,200 mile ride. I got one pulling into my in-laws' driveway. All but one from Goatheads.
We switched from the 32 mm Coninentals to 32 mm Schwalbe Marathon 420s, and found them pretty to be good all around tires. We have had 32 mm Schwalbe Supremes for awhile but have not really given them any hard use yet,about a 1,000 miles. I did destroy one on the first week I put them on my bike. I booted it up, and it got me home.
Marathon Supreme