I just went through this as I had a huge ecommerce site migration in January and then added a huge amount of 301's upfront with a regular dose of 301 updates as the 404's came in that I missed.
I didn't see any negative results from 301'ing the 500 pages and then the several hundred after that but that might be due to the fact that I redirected them to pages that were filled with the same content or associated with the same content (i.e. - category of a product instead of a list of the product variations page).
I've found my optimized pages were sticking a lot better and our new pages were being indexed quicker (90%-95% of sitemap urls are indexed).
A few things I was careful about when doing this was that I didn't just redirect to the home page. If the page didin't exist anymore and there wasn't any associated content I would just let it die after making sure there weren't any inbound links or onsite links to that page.
I can imagine that if you redirect 1100 pages of your site to the homepage it is going to hurt some of your site architecture as Google sees it and could therefore reflect in how Google or and other SE sees your site. Cleaning up your site is one thing but just redirecting to the homepage is another.
Try redirecting to a similar page, repurposing the old page (add a few links or a suggestion to the content "This event has ended and it was a huge success but check out our future events over here").