I agree with this thread 100%.. Simon, you have a fantastic plugin and absolutely understand the frustration on trying to please everyone.To make a plugin sustainable I think you made the right choice to have it with featured addons that are paid for.
You only have to take a look at Eventon Calendar plugin, he is the top selling author for events and calendars here in CodeCanyon. He has one plugin and features 6 additional extensions to purchase. This is what makes your work a sustainable model.
The addons that you had for sale were basically advanced features rather than updates to the plugin, so other users really need to appreciate that these are features that you can simply addon for a small additional cost if they need them.
Awesome… thanks for the new post and moving it out of the Ultimatum one. Now we can ask the Ultimatum people to post about Ultimatum here… ROFL.