We got a tandem, because our older sister was not at the fitness level we were, and could not keep up. Also, being a technophobe, she panicked at the thought of using "all those gears". With the tandem, she now goes everywhere with us, and doesn't have to worry about when to shift. For more seasoned riders, a tandem will be a fun change. The only problem is deciding who will be the "captain" (the front rider), and who will be the "stoker" (the rear rider). Tandems start at around $600, and go up from there. Try a couple of different models in our spacious parking lot, and feel the differences between price and component levels, and the weight differences between steel, cromoly, and aluminum. We carry tandems from RALEIGH and SCHWINN.
On a decent tandem, you will be faster than a single rider, and go up hills easier, too. Aluminum models are so light that one person can lift them on top of a car, to mount in a roof rack. Child trailers and trail-a-bikes will hook up to them, so that it can be a family outing. There is a family I have seen several times along the Fox River Trail that has a tandem, pulling a trail-a-bike, pulling a child trailer. It is as long as an eighteen wheeler. Ha-ha!!
So join in the fun!!