Would be interesting to see what people would 'pay' for.
Say CW would offer a 'bugfix' membership a 'content' membership and a 'features' membership all separately. Most probably viewed over a say 3 years period the percentages of purchases for each category will end up pretty even.
I personally feel that the timing is what annoys me (a little): Content can be delivered monthly. Fine, it's not part of the sonar-core programme, mostly bugfree and I can choose to use it or not. Features could be added 2 or 3x per year...that way my system is not "changing monthly". Bugfixes do not need to appear regularly at all, that is....they can be released as soon as the releases/fixes have been tested extensively and are most likely NOT introducing new bugs!
That way I don't have to worry about being faced with a potentially unstable system every month. As it is now I've been skipping every two updates but also been missing out on the content/features to play with.
(Just my opinion right now....subject to change by other good arguments :) )