Like ecmedia mentioned, you should create content for visitors and not search engines. On the pages that are not receiving a lot of traffic, ask yourself if they are useful to visitors? If so, do they have lots of unique content on each page? If they have plenty of unique/fresh content then I would keep them. If they are "thin" pages you might be better off consolidating the content on those pages.
I believe that you can use these pages to improve the rankings of some of your other pages. I think you can do this by putting related content on these low traffic pages and internally link them to you better pages. Also, I think that Google may factor in the total amount of relevant content on the site as a whole - the more, the better.
This is a great question, and while I always hear strong opinions either way, I have not seen a definitive answer. I think Google frowns upon having a lot of 'template' pages that are just blank, or use widgets to provide content, but the fact is that large UGC sites will almost always have those types of pages.
If it's not broken, don't fix it... If it is broken then figure out what's wrong before you do anything.
I think the reason there are so many differing opinions on this subject is it's fairly site, content, uniqueness, actual usefulness to visitors in the situation and context of the site specific. What 'works' for someone else in their situation is not guaranteed to 'work' for you in your situation.
I don't if I entirely agree with that. Why would I want link juice for "un-useful" pages? I would rather improve the content of those pages or remove them. If I'm getting good traffic to my useful pages, my goal would be to continue to improve the percentage of pages that are useful. It's pretty hard to go wrong with that strategy unless of course you are a poor judge of what is useful!