I’m all for seeing some Umbraco add-on’s but unfortunately the structure does not lend itself to templates. I’m sure you know what I’m referring to, the system has almost no default design or content structures, allowing you to define them yourself. This is a huge part of the power behind Umbraco as it’s completely configurable to your specific needs, however that flexible architecture is also the reason you can’t turn on/off any design you want the way you can with WordPress.
If someone designed a good content framework for Umbraco first, similar to what the “Creative Website Starter (CWS)” does, then you would have an established set of standards for themes to tie into and you would be more able to create design templates. Right now I don’t know of anything other than CWS that makes this possible. It sounds like a package waiting to be written if you ask me.
Packages are a different story. You could easily sell those on CodeCanyon.
I dont really know the cms but when looking at the download statistics from last year I dont think that it really appeals to the mass market. Currently you can easily make a living of wordpress templates, you can try to make one by selling joomla and drupal but then the air is already getting really thin I would say
Stats from the 2010 Open Source Market Share report:
If you put the cms download numbers in relation to the themeforest earnings you will see that they correspond. the highest grossing wordpress theme grossed about 10 times as much as the top theme from the joomla section. I am sure I dont need to do the math for Umbraco