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I think Egol covers it very well. I would not be changing pages if at all possible. What I would be considering is how to get the benefit/value of traction of 2015 pages for 2016 events. There are several options. But it could be a revamped page, a CTA which you can click on to go to 2016 page etc.  Also if no page up yet after every 2015 event, you could put on the page "the 2016 events details are not known yet, however leave your email and we will contact you with details of the new event etc" - that gives an opportunity to collate details. You know your business better than anyone, so likely better strategies but the underlying principles enunciated by Egol is the way to go.

Our site hosts b2b content and while I agree with your scenario in general, we do have some niche content that some users would have no interest in. A better example instead of a toy industry site might be a construction industry site. Let's say our content is generally related to the construction industry and our readers work in or own construction businesses. We might have brands and individual publications that cover everything from concrete innovations to lumber pricing to interior design. While all of the content is generally is related to construction, most interior design professionals may have zero interest in lumber pricing. That's essentially where we're at. For branding purposes the interior design folks think it would be better to have their own uniquely branded website, but they'll obviously feel the pain of the break from the main construction site.

You'll have more content on the page if it's not gated, but it's really difficult to say one way or the other at this point when comparing the non-gated page versus the gated one. Testing between both types, non-gated would give you a good idea via Analytics.

You should have migrated the sold domains "authority" to the new site using Google Webmaster Tools. Doing this would have transferred all of your SEO to the new site. However, since this was not done (or 301 redirect each link to the new site), i'm sorry to say that you'll need to start over

We typically use this model for most of our other event sites and I would agree. Thanks!

Thanks!

Splitting content off to separate domains is not a 100% no-no. I would only do it if the content is targeted to significantly different market or user segments, though.