Ulrich,
Much like your map, I'm using free mapping tools from Google. They have a mapping app that writes back to your choice of Google Docs or Google Fusion Tables. I went with the fusion tables, for a number of reasons, but mostly because it has native KML generation. In fact the KML link allows you to use Google Earth, which is an even cooler view on the data than the browser.
Harvesting the links off of GCA.com, getting the course URL, tracking down year and archtitect, and placing the location is all by hand. The markers often align with Google's place markers, but when there's ambiguity, like at Pinehurst, I try to figure out where the course starts and place the marker there.
I like that you have an underlying data model that you publish; I believe there's an opportunity to develop an open resource of GCA material, and for the structured content having a robust data model is key. It looks like you have a good model. I haven't researched the free cloud development platforms recently. Salesforce.com had a low price platform, and if you modeled your app as a community rating and CV tool where individuals build up shared data, like the courses, augmented with their personal content, rounds, you might find the expense is worth effort. You might also find that if you can get a mobile face on the data entry, so users can record on course, you would get more adoption. Mobile and cloud is where it is at!
Your map is pretty cool, too. I like how you have a photo in the information window. Very nice.
Dave