Lots of choices ...
A Flying Scot or something like it will certainly give you a lot more ... the opportunity to take guests sailing, a longer season (because it's not as wet as a Sunfish), easy singlehanding under mainsail alone, etc. I sail a Scot and love it, but there are plenty of other choices available in boats under 20 feet. There have been two recent threads on this, and a quick search will give you lots of other options. If you want to chat further about the Scot, don't hesitate to drop me a PM.