Hi onlinegusto,
I endorsed Jordan's answer because I felt that it was a succinct answer to the question. I dounderstand how and why the response wasn't satisfying to you, though, so I'll attempt to address your question in its entirety.
**Does the Spam Score generally take long to drop? **That depends. As Jordan and I have both noted, Spam Score updates along with the rest of our link metrics with each new index. When your Spam Score updates will depending on when, and even if, the latest crawl indexed your site. I recommend reading this Help Hub page on Mozscape updates to get an understanding of how that works.
I also recommend reading Rand's post from the launch of Spam Score, which goes into those 17 factors. That could give you an idea of the sort of things that could be giving your site that score of 9/17, which in turn could give you an idea of what you'll need to do to bring it down.
**Should I try and stop the permanent redirect and direct my .com to the .net domain? **Hard to say. Though TLD is considered in Spam Score, it only considers TLDs highly associated with spam to be problematic. That's not the case for either .com or .net, so the simple fact of your TLD isn't a factor in your site's 9/17. If one or the other has a lower score, feel free to use that one, but be mindful of the other SEO issues that could arise.
Are there experts who can lower my score? Also hard to say. There certainly aren't any experts I'm aware of who focus specifically on lowering Spam Score. There are experts who focus on penalty recovery, but I see no indications that your site has been penalized. I can't speak for the entire community, as members contribute to these discussions on their own time and without compensation. There isn't any directory of community members and their specialties.
It's worth pointing out exactly what Spam Score measures. The 17 factors are correlations, not in and of themselves indicators of spam. I'll let Rand take it, from the blog post I linked:
The overall Spam Score is currently an aggregate of 17 different "flags." You can think of each flag a potential "warning sign" that signals that a site may be spammy. The overall likelihood of spam increases as a site accumulates more and more flags, so that the total number of flags is a strong predictor of spam. Accordingly, the flags are designed to be used together—no single flag, or even a few flags, is cause for concern (and indeed most sites will trigger at least a few flags).
To lower your score, the best thing you can do is focus on the particular flags that you'll find in the Open Site Explorer report. And, of course, to build high-quality links.
**Should I look for non spammy niche directories in its niche and submit my site to them to increase link authority and nofollow links? **I would never recommend any link directories as a means for building your link profile. They're very unlikely to help in that regard. They _may _help by driving a certain amount of traffic to your site, but that will do very little to help with Spam Score or authority.
So, to summarize:
1. Spam Score updates along with the Mozscape index, so it could take some time to see a change.
2. As—at least partially—a link metric, Spam Score can be improved by building a quality link profile. That could include disavowing your own spammy links, but please be careful if you decide to do so.
3. Making positive changes on your site will lower your Spam Score over time.
Please be empathetic to Jordan and me and understand why we both felt that his response provided an effective, boiled-down answer to your question. Good luck, though! I know how frustrating it is to see a metric like that with no apparent way to improve. 
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I'm so glad it helps.