This came up a while ago, and we had a bit of a debate (I thought it would be less too as you say), so I wrote to SW and asked them (you can tell I am busy- lol). Their answer:
Dear Claire, Thank you for your recent e-mail.
Sadly cooking with alcohol does not change the nutritional breakdown of it in any way; therefore the Syns will remain the same after this process.
Wishing you every success with your weight loss journey