I have both a Tomcat tandem (7 years old) and a Sawtooth 1, which is also plenty big to use as a tandem. The Sawtooth is an amazing touring IK, and will simply run circles around the Tomcat out on a lake. I have added the skeg pocket to my Tomcat myself (very simple), and it does help a lot for touring. It works just fine for flatwater, but it is really designed as a whitewater boat with a flat, stable bottom as opposed to the V-shaped hull on the Sawtooth. The Tomcat has been down pretty much every major river in Oregon and Idaho (with the skeg removed, of course), usually piloted by a kid or a novice, and has performed flawlessly. Sure, it's been flipped a bunch, but that's part of the fun. I've never had to do any repairs, and other than some fading from the sun (even with copious amounts of 303 the first gen. red Tomcats you see out there are all pink colored now). For the money, I don't really think you can beat a Tributary, and for how you plan on using it, the Tomcat Tandem would be an excellent all-around choice.
Check out The Boat People - Inflatable Kayak & Raft Specialists
website if you want to read up on IKs- their website is a treasure trove of good information on most of the options out there.