1. The course is good, quite comprehensive, certainly worth doing but in my opinion, not worth the money it costs.
2. If you want to earn a good living, you almost have to be self employed and not working for someone else.
3. No matter what your qualifications are, unless you have the ability to advise and interact with your clients on a commmercial level, offering sound business and marketing practice advice as well as being able to deliver and maintain web content, you're goosed.
4. Making big bucks from the web is harder now than it has ever been and so-called webmasters are fast becoming a thing of the past in terms of the vast salaries they used to command. This is a generalisation but is broadly true nevertheless, at least on this side of the pond.
5. Qualifications are no substitue for experience and vice versa. Ideally you need to have a balance of both to be able to do the kinds of jobs the course would have you believe will be the end result of passing it.
Personally, I don't think that it is worth the asking price unless a parent company is paying it for you. Self-funding through it will not guarantee a startlingly huge salary at the end of the course, but this goes for any qualification.
Think of it like this; how many webmasters/site maintainers are already out there doing variations on a theme ? Some are good, some are bad, but they all have one immediate advantage; they are already in the game. Breaking into this field is harder on an almost daily basis and those who are currently involved in providing web services generally find that they have had to diversify to one extent or another over the last few years. You certainly can't command the prices that people were prepared to pay just a few short years ago for web design or mastering.
If you are happy about tackling the nuts and bolts of at least two programming languages and internet, intranet, general networking, design, implementation and so on go for it. You can do all of that without taking this particular course though.
Keep one thing in mind; the web is built by specialists who work through site designers who can either find the work or who enjoy a position where the work finds them. I call on the services of some very capable freelance programmers for certain projects - especially very large and complex database projects. They charge a healthy premium and so they should given the level of their skills, but they are not full time employees and their services are not often needed. This is despite the fact that I am a software developer and teach software engineering. Quite simply, I can find the projects to work on but sometimes need skills far more advanced or specialised than my own - using languages with which I am not as familiar for example. This is the way of the web and I don't see it changing much.
Sorry if this sounds doom and gloom, but there are no guarantees of the super jobs you could get after doing any course.
I agree with one of your comments in particular; "I think £3000 is a lot of money". It certainly is, with no guarantees at the end in an increasingly competitive markplace.
I'm not saying it's not worth doing, but it is worlds away from what you currently do and no matter whether you are MCSE, MCP, CISCO qualified or whatever, you will have a very steep learning curve ahead of you.
Best of luck no matter which way you go with it.