IO540,
As you quite rightly point out Cardiff isn't closed to visiting GA although as far as I am aware the main, if not only, GA handling agent is Signature. Aviance are also on field but they tend to deal with the likes of BMI Baby jets.
The flying club ceased trading a couple of years ago but Aeros (of Gloucester) are opening a base at Cardiff on the 1st June in part of the white building in which the previous flying club vacated (southside of the airport).
I presume the NOTAM will dissapear at some point and GA will once again be allowed to park south side and enter/exit via the flying club during opening hours.
Fingers crossed as I would dearly like to fly my own aeroplane down to visit my parents but am loath to pay Signature handling fees when they are quite expensive and basically the only choice for GA at Cardiff.
The restaurant upstairs in the white building (flying club building) is still open for business so that'll also be quite useful for when the new club/school opens its doors.