Hi StratosJets,
In general the more pages you have the more content you have. More content is usually a good thing. I think before anybody can give you a solid recommendation we would want to know why you are wanting to remove 10K+ pages from the index.
You see, Google looks at your website like a splash of paint on white canvas. Your website in a whole is going to have a large splash around your main pages, then some secondary splash clusters around other content types. Just because these secondary splashes aren't performing as well as the main splash doesn't necessarily mean you want to remove them, as they help paint a picture of the complete site.
If the purpose of removing pages that are driving "some" traffic is only to try and boost the other pages I would say don't do it. You maybe able to restructure your navigation so that these smaller traffic pages don't get as much link juice as some of your higher performing pages. I know this can be a bit challenging in some CMS suites, but removing pages that are bringing in traffic only to try and boost other pages is a very advanced SEO metric and should really only be tackled when you have gathered lots of data.
Imagine you remove 10k pages that on average get 2 hits per month each, are you reasonably sure that the remaining 2k pages will generate 20,000 more hits once those pages are gone? Or is it more likely you lose those 20,000 hits along with the traffic patterns those 20,000 hits would normally bring in?
That being said there are cases to be made for removing pages, specifically ones generated by CMS platforms.
When is it okay to remove pages: The general rule here is if the page has no value or negative value for your viewers / customers.
No value pages: These are pages that have been redone, or their content is also available on another page which is more in depth and/or more user friendly. (Thin Content type pages)
Negative value pages: These are often generated by CMS sites, eCommerce CMS's may have auto generated pages like "Manufacturer Info" or "Item Review" pages, which you aren't using. Blog sites may have "Monthly Archives" or "Similar Post" pages which can create duplicate content if not used correctly. These pages can confuse your users and search engines as to what your site is really about.
If you find your site has tons of no value pages and negative value pages I would say okay go for it, but be very careful look at your page metrics, be sure the pages you are removing are in fact useless and provide no value for your viewers / customers.
If you decide to go the route of removal, the best way from my experience is to 301 pages which have correlating content on another page, and only 404 any page that have absolutely no value and page alternatives. If you 404 a page make sure you remove it from your sitemap and try submit it for removal. Lots of 404's isn't a good thing either...
I hope this helps,
Don