Digestive enzymes can help if you have issues with digestion. Otherwise, I wouldn't put much stock into them. I would just opt for a daily probiotic instead.
GDA's are very useful, especially if the meal is carb heavy. Not only will a well dosed GDA help with shuttling nutrients, but they can also help give a full look to your muscles after the meal and provide a pump, if used pre workout. Personally, I can eat a meal well over 1,300 cals and if I take 2 caps of SlinMax 15-20 minutes prior to the meal, I feel like I could eat even more.
Here is how I would address the second portion of your post. I wouldn't skip meals the next day. Hell, if you're cutting, the single meal may do wonders for your leptin levels. You could also just eat slightly less the next few days or do a little extra cardio. But like you said, we all have weddings, birthdays, etc. That is life. Unless one is competing or getting ready for a photo shoot, I would just live life and not worry about offsetting that single meal. Think about it this way, if you have 5 meals per day, that is about 1,900 meals a year. If you over indulge two times per week, you're looking at 104 meals or so. That is not going to make or break one's physique.
However, again, I do like a GDA either for cosmetic purposes, a pump or even to reduce bloating.
