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Do I have anything to gain by allowing these comments to stay on the page? Probably not.... and if those links are going to bad neighborhoods you can expect your blog to tank.

What is better? Singular vs Plural? We tried putting keywords that is singular but there are many other plural keywords  within that landing page. Now that plural keyword is outranking the singular. What is the best practice for this? We want the singular keyword to rank higher the the plural? thanks

I see what you mean, so you have a bit of a unique situation. Have you done keyword research? Do you have an idea of what you really want to rank for based upon search volume etc? Do people search for these specific product names and variations?

I have the same exact problem and I could not find a way to prevent them from being crawled so I came to a path with 2 decisions, attempt to redirect or fix these pages, or document them and ignore the warnings. I chose the 2 path just because it made more sense.

Remember that a Warning is just that, a "Warning". This doesn't  necessarily mean that you are doing something wrong. It just means that you should be aware of a "possible' issue. If your navigation is intended to help visitors navigate your site and facilitates finding products, then I wouldn't worry about the warnings. If you have such a large navigation just for the purpose of stuffing keywords, then I would reconsider the strategy.