I guess for some people the dealers are important and for others no to much. Todd, in your case you are a very well infomed person with access to many products and extras so definetly a dealer will not do much for you in some areas...

But in general what can a dealer do:
1- Deal with all comunication with the factory, making sure questions and customer requests are answered. This is not always easy for customers who go direct.
2- Give customer support in case any aid is needed in building, CG, throws, first flight, etc.
3- In case of problems which require a warranty claim from the factory the dealer will be of far more weight with the factory than a single customer.
4- Give good customers a discount price.
5- Participate on events promoting the brand.
6- In case of problems not affected to warranty help customers get all the necesary parts asap. A good dealer should not make a huge margin on this as there is not really a big market for replacment parts, the bussiness is on selling the kits not the replacment parts, this should be looked as a service more than a bussiness in my opinion.
7- I am sure I forget a few other things....

In general when orderring replacment parts it is better to order exactly what you need, if you just need the retract air cylinder, don't order the whole retract it is going to be much more expensive. If you are specific on what you want you will find out that replacement parts are not always that expensive.

In general terms a good dealer is one that is on the customer side and will help them get what they need. The factory can't handle to go direct worldwide it is just too much information and customer requests to handle, remember the US is not the only market and sometimes it is not even the biggest for a company, so having to deal with every customer is not always easy for a factory. A good dealer network will do the job easier and more quickly.