Is there a difference between sloop with spinnaker and sloop without ?????
if so you'd need an additional 2 days.....
I like the idea you've proposed... in theory those keen enough could race in each class
days 1&2 setup and race for sloop-rigged c/ship
days 3&4 setup and race for sloop-rigged spinnaker c/ship
days 5&6 setup and race for cat-rigged c/ship
days 7&8 setup and race for cat-rigged spinnaker c/ship
Imagine if one boat took out all the c/ships

Another way of looking at it is you could also have it set so each class counted towards a general overall championships...
so you'd have:
champion of cat/spin
champion of sloop spin
champion of sloop
champion of cat
&
best overall Mosquito
one busy week of sailing...... but hell worth it