Yes. Absolutely correct. You should never index tag pages. These may be targeted but are of low quality with not much quality content. Moreover, they may have more keyword density than what you should have for a page to rank.

I have an article on that here. An extension for firefox called Dust-Me selectors can help you identify unused CSS on multiple pages. It tracks all the pages you visit of a website and tracks classes and ids which were never used. Moreover, you can also give it a sitemap and it will figure out the CSS which was never used.

The best part of adding the noindex tag is hiding the pagination pages from the search engine's search index, which will make only the highest quality pages available in the search results. This gives a signal of your website being a better one with good content. The CTR rate will be higher too.

I have a plugin that automatically adds rel="nofollow" to anchor tags that link to external websites. Now I want to make a particular link to override that nofollow tag and pass the page juice to it. How should I go about it? Will adding rel="follow" help?

Yes. Absolutely correct. You should never index tag pages. These may be targeted but are of low quality with not much quality content. Moreover, they may have more keyword density than what you should have for a page to rank.

I have an article on that here. An extension for firefox called Dust-Me selectors can help you identify unused CSS on multiple pages. It tracks all the pages you visit of a website and tracks classes and ids which were never used. Moreover, you can also give it a sitemap and it will figure out the CSS which was never used.