Kaferhaus, excellent review and a good reality check for anybody who might purchase a sail kit expecting the PA to turn into a "sailboat". The sail is too small, the mast is not rigid, there is no performance related rigging and the system is not optimally balanced. None of Hobie's sailing kayaks (except he Adventure Island) are really designed to compete with single purpose sailboats. But, as you said, it's fun.
IMO, the best use of the sail is in a hybrid mode where you're pedaling while sailing. As a supplement to pedaling, the sail allows you to gain some decent speed without having to pedal very hard. As a supplement to sailing, pedaling upwind makes windward performance viable. This combination works particularly well with the PA -- the extra speed improves both rudder authority and tracking. As an old sailor, it took me awhile to warm up to this concept and I was reluctant to mix sailing with pedaling. Eventually I learned, especially in lighter winds (and while tacking in heavier winds) that it makes an excellent combination.
A couple of specific comments -- the mast is designed to be "bendy" in gusty winds as a shock absorber and safety valve to dump air for the narrower kayaks. On the sailing forum there are lots of rigging tips like stiffening the mast, adding a "boombat", reefing the sail, adding blocks and cleats, adding jibs, daggerboards, leeboards and even enlarging rudders. There is definitely an upward potential for the sail if one is interested in pursuing it.
The PA is decent at lean-steering -- by leaning (or heeling the boat) left, for example, the boat turns right. This is a pretty good thing when it comes to augmenting steering. When sailing though, any heeling accentuates the weather helm, so in heavier winds, keeping the boat as level as possible by hiking out really pays off in terms of rudder authority.
For any serious sailing there are probably better bargains around. But for adding some fun and versatility, extending your range or just relaxing out on the water, the sail kit is a nice option to have.