I drive a 2018 Airstream interstate extended version. I bought new. It is pretty. It's fun to drive. BUT..... all the bells and whistles means there is always something needing attention. If you buy new, count on spending time getting warranty work done. And where are you? Where are you getting work done? Not all Mercedes dealers do service on these rigs. Even ones that do don't always know what they are doing. I ended up driving back and forth from SC to Ohio to the Airstream factory. When you go to the factory, they have all the parts and get everything done, but they are booked. I make sure I have an appointment booked every year...just in case. BUT......with 2 different companies...Airstream and Mercedes, sometimes you go round and round about who's responsible for what. For example, the camera system is Airstream...but it's tied to the safety system that is Mercedes. If you get Air ride suspension, which you definitely need...that's Airstream and they removed all the standard Mercedes suspension to install it. Today I spent all day at a solar installer because Airstream won't look at anything they didn't install. They weren't installing boondocking packages when I had mine done so now I have someone else I work with. I highly recommend you have solar and lithium batteries in the Interstate if you are going to be sleeping in it.
I do consider the bed comfortable. If you use the shower, it's a wet bath...you basically sit on the toilet and shower. That's the biggest complaint. And it's what they call a "navy shower". Rinse, turn off water, soap up, turn on water, rinse. You can easily fill your gray tank 30% with one shower. And, there's no hot water tank. It's supposed to be "instant hot water" but it's not so instant. So there's waste waiting for hot water. At campgrounds, I usually use their showers.
Mine came with Garmin RV navigation system. I have not been happy with that and mostly rely on my phone. It is not always as quick to pick up accidents and road closures like my Google. And it sometimes adds 20-30 extra miles to a trip.
Others mentioned being handy and doing things yourself....yes, you can. There's all kinds of YouTube how tos...BUT...more often than not, it's quite the challenge. Many times you are trying to work in small spaces with limited lighting leading to abrasions on your knuckles, blood and band-aids.
Test drive it on the freeway! Listen to all the noises. You are hauling a house. It's not a quiet luxury ride. Sometimes it drives you crazy trying to figure out where a squeak is coming from; sometimes you barely notice.
Where will you park it. Even if it fits in your driveway, you may not be able to park it at home. I just recently moved to a property where I could park it. I was tired of dealing with the HOA and tired of paying for storage, so I bought a house on 2 acres. You buy for some degree of freedom, but you don't always get freedom and it's a high price to pay for the freedom you get.
Whatever you buy, there are forums for your brand. Even tho you haven't bought yet, you can look at the Airstream forum. You can post problems, questions, etc and get feedback...most of the time very quickly. Also each brand has Rally organizations. My first year I did several rallies and met other Airstreamers. I enjoyed meeting fellow airstreamers very much. I've definitely had a few headaches and a few days of total disillusionment with my Airstream, but I'm not ready to give it up yet. Good luck and safe travels!