The RAV4 is a good SUV type vehicle, I know a few people that have them, not one serious complaint from any of them.
Im just saying that when it comes to comfort and design, it does not compare with the Mercedes, but then, its not supposed to.
I would certainly go with diesel, 100k on a well maintained diesel is pretty much just broke in. People on the Diesel forum I frequent are showing 400k+ and still towing with their GM and Fords (dodge not so much)
That Tacoma you have should last well into the 200k range if its taken care of, and I suspect it is. Matter of fact, Toyota is introducing a new 1 ton DRW with a diesel that I think is going to take a big market share from the big three in that area. Mileage estimates are a bit low for it however.
My 3500 now has 62k on it, still has that new truck feel to it (including the feel of every pebble on the highway) as far as creature comforts, other than ride quality, the Mercedes has nothing that my truck doesnt have. I have A/C with personal controls for driver, passenger and back seat riders, I have the tv/dvd, all the gauges, sunroof, memory seats, heated seats, XM and Onstar Phone etc... and to me, its more comfortable to ride in due to the size inside. Parking it at a store is a pain in the ass though.
The main advantages of the diesel are power, torque and mileage. with my 3500DRW on the open road (not towing) I average right around 23~24 mpg, weekly back and forth to work I average around 18.
Wifes Jetta TDI is coming in with a solid 49 mpg back and forth to work for her. long highway trips we have seen 59 mpg. Comfort is good once you are in it but the in and out process requires a shoe horn and some silicone spray.
I just like big pickups, if you have a pickup it should be able to carry or tow anything that you think you might want to throw in it or hook it up to.
so, take all of my thoughts into consideration given the choices presented, I would seriously look at the Mercedes, but I would see if it came with a diesel option.