My old club suffered the same problem. We solved it by offering a triangle course and windward leeward course. Cats racing a windward leeward course would just ignore the wing mark and sail a few extra laps.

Div 1 - 14 footers - Triangles
Div 2 - boats above 14 feet without spinnaker - Triangles
Div 3 - Spinnaker cats (or those wishing to race WL) - Windward / Leeward

Boats such as A Class and some Taipan 4.9s would join Div 3 for the WL course. N5.8s whilst they are reaching machines are also very good WL boats.

We offered 2 x Club championship series consisting off Div 1 and 2 in the 'Classic Div' and Div 3 in the 'HP Div'. Boats such as A Class, N5.8, T4.9 would have to decide weather they wish to compete the season in Div 2 or 3.

This kept both groups happy, however it was important to advise all boats of the dangers when and DIV 1/2 boat is rounding the top mark under a boat racing WL who plans to bear away to head down the course.