Demented I would do it how you suggested. Flexible syns are a tool to use when you KNOW you will go way over your allowence - like a special occassion. The idea being if you keep track and some sort of count you still feel in control, and the next day you can go back to the plan. It is great to use very occassionally as you can't just sit there with nothing to eat. Also it absolves you of the guilt that usually follows the pigging out. The 'Oh no I've ruined my diet, I may as well give up!' type thoughts.
A few glasses of wine on a Friday night is fine to save syns for. I used to use my syns for the week 70 and take a bottle of wine as 35, this means I could drink that bottle in one go, or throughout the week. I would then stick to 5 syns a day. I am not a chocolate freak/crisp fan on SW therefore this wasn't a problem.
Sucess Express sounds interesting, although I only do green days, but it makes sense to limit the potatos/pasta/rice to 1/3rd of a plate. It just depends on teh size of plate!!