I think they're dirt cheap for what you get compared to the cost of standard training.
£120ish for a full mornings training every sunday for a year. It cost me £70 for each lesson for DSA test training.
EDIT: The enhanced rider scheme is an expensive way of doing things and I'd go for the IAM or ROSPA myself. Bikesafe days are good so I hear but I've never been on one.
If you want to see what advanced riding is all about then get yourself a copy of Motorcycle Roadcraft - reading and applying this will make you a better road rider. A lot of it will be obvious to you, but some of it will make you think differently and ride better. It also help you link up and consciously apply seemingly obvious things which you may not have been thinking about before.
Another good source is Roadcraft Nottingham on Youtube - he has some good videos on advanced riding that will give you an idea.
As for whether advanced training will help you - the best upgrade for your bike is to improve the ability of the rider. Whilst you might have problems with some up their own arse people in the IAM or similar you will be in no doubt that there are some cracking riders in there and they are well worth listening to.