I will go ahead and assume that you just hastily skimmed my post. If you go back and re-read what I wrote you will find that what I did actually write is that if you are in a highly competitive field then an extra keyword may make a difference. If you are not in a highly competitive field, thus a niche by my definition, then that difference is for practical purposes irrelevant. What really does make a difference in rankings is content, no amount of SEO magic is going to make up for lack of substance.
SER are only meaningful if the person performing the search is not aware of your resource. Here's what I mean by that: Let's say you are looking for <insert search phrase here>. You type that into Google and Google returns a bunch of results including those from online forums. You will notice that Google bunches forum posts from the same forums together giving you a few threads as hits and then having a link that says "show more results from..."
Now a site that is 100% perfect from a SEO standpoint will still not be in the top results unless they have content that matches the search phrase and unless they have a lot of that content. Search no longer looks at static pages on their own, search now considers the aggregate weight of content that matches the search and essentially ranks pages by volume of relevant content. No amount of SEO will make up for having that content, and that content will trump SEO magic time and again.
IMHO way too much weight is placed on SER because people think that the first link in Google is the one that gets clicked. That may be true if the searcher is completely oblivious about the topic, it is far more likely that the searcher will click a link to a site that (s)he has at the very least heard of before. You can be the 5th link down but if the searcher recognizes the name of your site and associates you with being a known resource then (s)he will click your link instead of the first link.
SEO doesn't result in what you really need which is brand recognition. The name of your site has to be out there visible to potential clients. IMHO one gets a significantly higher value for one's dollar if one spends the cash on marketing rather than SEO.
At the end of the day though there's a very simple way to measure how important search engines really are. One can easily track down from where visitors arrive before they sign up to become members.