My wife and I started biking about 15 years ago with single bikes. It became a stress point because we use bikes as a form of exercise rather than recreation. For me that means 50 to 100 miles/day at close to 20 MPH. For her it meant 30 miles/day at 12 MPH. Touring was no fun at all because she constantly tried to cut the daily distance.
So we found Tandem bikes. First we rented with good results and bought a Cannondale Aluminum frame with hydraulic brakes. I seem to remember over $3,000. We are doing 50 miles/day for exercise at breakneck speeds and tour up to 100 miles/day. We have a lot of enjoyment on the bike and the consequential wining and dining and socializing.
I would recommend it to anyone and I am puzzled why not more people do it?
Only down side: The season is short around here and Florida is a long drive. Not easy to ship or fly with a Tandem. Perhaps, some day, we will just have to buy another Tandem for Florida.
BTW, yes, cost of maintaining and upgrading of a Tandem is not cheap. I just put up $1,000 for new brakes and gears with Shimano XL shifters. They are worth it.