You'll probably get some different opinions on this. Your site link architecture and the design of your archive/search/category needs to be assessed to figure out the best solution.

If I had to pick one or the other for the nofollow attribution, I'd pick the Archives over Categories because they have less keyword value. Generally, I'd say no need to use it. Sure, you might say that those pages don't have much value since all they contain is a repetition of content on your other pages. And some may try to use the "nofollow" tag as a way to prevent any link juice from flowing to those pages. But PageRank sculpting using this tactic isn't really effective.

It would be more effective for your SEO to redesign your blog/website sidebar/footer links so that you have "less" links pointing to your Archives and/or categories.

Using Wayback would be strange.It's just a quick WHOIS lookup to determine age.

Horribly inaccurate! Google hasn't provided much in the way of explanation. It use to be worse because the numbers were based on the combined volume of both the search and all their networks. They changed this some time in 2010. Here are some other considerations that affect your impressions volume:

• Is your bid and quality score so high that your ad is literally running at #1 ALL the time?
• Are your campaigns capped or cut off by budget or scheduled time to show?
• Do you have any negative keywords applied to the campaign?
• Are using exact, phrase or broad match? Google supposedly bases the volume on exact.

It is not wise to completely rely on the Keyword tool local search volume. The other metrics like total search results, and competition help craft a better keyword list for your campaigns. I also like to export the entire data set, and look to see how the local volume is changing over time. Is it trending up or down? Is it a consistent average?