I might have caught Kairouan on a bad day. I went on a Friday and everything was closed. The town was mostly deserted and I had no idea what to do, so I went with a guy offering me a guided tour. This proofed to be more interesting, than walking on my own and was a rather pleasant experience, apart from the last stop with the obligatory carpet shop (I specifically negotiated not to visit before starting the tour). With most shops and restaurants closed and almost no people, it felt rather weird to wander around the streets. I would also not be able to see the outstanding value of this town, compared to other medinas in the country I saw. I’d say it’s one of these places that due to proximity to the other WHS is a must for the real hunters, but can easily be skipped if you only go for the country’s highlights.
The town can be reached rather easy by car. Expect some narrow roads on the way if you come from the coast. I did it on an easy half day trip from Port El Kantaoui, spending the rest of the day at the beach. You could easily combine the day trip with Sousse and/or el Jem, if you have limited time resources.