You've gotten good advice on pretty much everything. I will add that I have a Pacific Dually that I got new and trued the wheels, put on a rack and added a longer stem and seat post. I also have a DaVinci Joint Venture that is a really great bike. The Pacific is kind of our preference for casual rides. It's heavy and a little sluggish in turns but the weight and geometry make it pretty stable. I wouldn't spend a lot of money on your Kent except whatever it takes to get the front derailleur to shift right. It sounds like you will be enjoying tandeming and that means you will have to upgrade. You may or not keep the Kent but you will get more fun for your dollar on a better tandem.