Thought this thread was so good I'd put my ideas in.
The Manx is only missing 2 fairly big solo classes and thats the big classics and the big modern stuff. If you go to any club meeting then the 2 main classes are the F600 and the Open Powerbike. The Manx has 600s but what other bikes can you use in the Senior? Big V twins and 750s? Hardly anybody races these anywhere else. There really is only one 750 available now in the GSXR and very few 1000 twins as new Ducatis are 1098. I know many are going to mention the safety issues due to the speed of big modern bikes but you can get into plenty of trouble on smaller bikes too.
The next thing to attract riders is to address the paddock facilities. Seeing bikes pushed to scrutineering with cling film on the wheels isn't sending out the right message. How many riders from this year will go home remembering not the awesome racing spectacle that it is but the Glastonbury like conditions?
Last thing the riders need help with is the cost. I think the entry is OK and represents good value for money for the amount of riding done but the ferry is extortionate. I paid close to £600 for my van and caravan this year. In 3 years of riding at the North West 200 it never cost me a penny!
Don't worry about trying to attract more visitors with discounts etc. As the film "Field of Dreams" said, if you build it they will come. Build a Manx GP with big classics and modern production bikes and it'll be very popular indeed.