Hi Daniel,
This is actually a two part question, so here's the two part answer.
Linking to a Target Domain
Google's core algorthim is based on linking. The quantity and authority of links are presented in the form of PageRank, which isn't displayed by Google in any useful format nowadays. Having quality links from quality 3rd party domains add credibility and ultimately ranking for the target domain. Earning links to a target domain to achieve maximum ranking is ONE strategy and can produce great results by itself.
Creating Additional Micro-sites for SERPS Saturation
By creating additional domains simply to achieve higher ranking for a target domain divides your marketing efforts and can add confusion to your link building and PR teams. However, creating themed experiences via micro-sites and micro-blogging platforms as a way to increase search engine saturation while also boosting link juice, can be a powerful strategy (especially for an online reputation campaign). Take websitegrader.com for example. It's a micro-site built on its own domain that drives massive links from people who enjoy the tool. Yet, at the end of the day it's lead generation tool and could be a great link opportunity had the Hubspot gurus considered adding a keyword-rich link from their grader properties.
So I suppose the best answer might be to do both:
- Build a powerful target website with the most influential links to earn top placement in the SERPS
- Build one or more additional domains with a specific, non-salesy, theme in mind to earn saturation and organic links.
Just don't forget to add the link from the micro-site at the end of the day, if that's one of the strategies you decide to employ.