We have been riding a Bike Nashbar tandem for 24 years - 26 in wheels and flat bars - and it has served us well. Many of the components have been upgraded over the years including converting it to disc brakes and then to 650b wheels. We are a upside down team (stoker taller than captain) and are finally upgrading to a custom Curtlo tandem which we can't wait to ride!
Enjoy what you have and then as you ride it more you'll figure out what does and doesn't work for you.