My traffic, and therefore revenue, are continuing to fall after Panda rolled out to other English speaking countries. I expect it to level out soon.
I think if you continue to publish on Hubpages you will need to choose more specific niche titles because hubs cannot easily compete with the more competitive terms as used to be the case.
Keyword research and onpage SEO are still very important. Getting quality backlinks to your hubs has become more necessary.
HP has guidelines on how many product ads can be displayed now. 1 per 50 words.
As for external links, just make sure they a useful to your reader and don't go overboard.
This forum thread might interest you: http://hubpages.com/forum/topic/73129