I have to say that riding at a closed resort is a great idea. You've got the runs, and trails to get you in there. Generally speaking, it's easy to avoid avalanche prone areas at closed resorts. Berthoud Pass used to have a ski area and a lot of what I do there is on the old ski runs. There is a lot more to it than that too, but it makes for a great starting point.
You can probably convince me to head back up to Fortress again this year. We wasted so much time hiking up I didnt get a chance to properly explore the area. The snow conditions are better than they were and we have had a bit of snow the past few weeks. I wouldnt mind trying it the next weekend there would be some fresh snow.
I think this would be a good chance for me to rent a split board from the Uni and test one out to see if I like them. My long term pipe dream would be to get a custom split but I want to get out there sans snowshoes to see if it is what I expect.