So I came up with some custom CSS and HTML for a project that ended up creating a bunch of repeated anchor tags in the HTML mark up.
This markup involved image mouse overs, so it's not like there was an obnoxious amount of affiliate links on each page, that's just how to the markup had to be coded to achieve the CSS effects I wanted with out using JS.
This wasn't my intention, but I ended up with a few pages that had as many as about 70 nofollowed affiliate links.
I've seen plenty of sites that have about 40 or so anchor tags that were affiliate links on one page and those pages ranked just fine, so at the time I wasn't concerned about it.
I gave up on the site as it was not performing well and I finally got around to trying to figure out what was going on.
When I mean not performing well, in my experience it seemed like something was pretty clearly wrong with the site.
I didn't have any rankings on page 3 or higher, even on extremely specific phrase match keywords, that the content really should be ranking on.
So to test, I removed the mouse overs on one page, which cut out about half of the anchor tags, then I cut some additional links out.
For the first page, I added a bunch of text and reworked the page, which obviously skewed this test, but I was about half way through doing the changes I wanted to do, I saved the page and went to bed.
Overnight I guess Google Bot came by (verified in my log) and re-crawled the page.
I had no plans on indexing the page as I wanted it to be a good test, but I requested index on the page and with in 20 or so minutes, my ranking basically went up by about half of the number of positions the page was before.
The upward bounce up could be caused by request index, but I generally find that the page will return to about that position later on, even if it drops a day or two after pressing request index.
So, I tested another page, this time only removing the extra affiliate links, then requested index.
Approximately the same result occurred and the page jumped up dramatically, about half of the number of positions again.
So, does having excessive affiliate links/nofollow links hurt SEO?
To me it would seem so.
This isn't a 100% perfect pure isolation test, but I'm more concerned with my site performing and not trying to figure out what exactly Google didn't like.
It's possible that it just doesn't like my mouse over code, but somehow, I doubt that.
Edit: Added a GA screenshot. Obviously a pretty night and day difference in the impressions. It looks like it's going up further today as well. I'll probably start working on it again now that the issues seems to be resolved.
I have no plans on doing that. The pattern is clear enough to me, if it isn't for you, then I suggest you come up with a test that satisfies you.
Edit: And no, it's definitely not what I wanted to find. I would much rather have found out that it isn't true, as that requires much less work on my end.
This sounds like a lot of "I found what I wanted to find" versus any kind of concrete evidence.
If you want to prove that longer content ranks better, you would need to setup multiple domains with pages targeting the same keywords and put content of different lengths on them. Obviously, you are introducing tons of other variables when you do that, so you would have to do it a few thousand times to have any kind of reliable "evidence".