Keyword rich domain names -> Point to sales funnel sites or to landing pages on primary domain?

[Transpera]

Hey everyone, 
We have a tonne of old domains we have done nothing with. All of them are keyword-rich domains.
Things like "[City]SEOPro" or "[City]DigitalMarketing" where [city] is a city that we are already targeting services in.   So all of these domains will be targeted for local cities as keywords.

We have been having an internal debate about whether or not we should just host sales funnel pages on these domains, that are rich in keywords and content.........

... Or ...

... Should we point these domains to landing pages on our existing domain that are basically the same as what we would do with the sales funnel pages, but are on our primary site? (keyword rich, with good and plentiful content)

Then, as a follow-up question...

Should these be set as just 301 redirects on these domains to our actual primary domain so the browser sees the landing page domain instead of the actual keyword-rich domain? ( [city]seopro.com )

Thanks guys. I know for some, the response will be an obvious one. However; we have probably way over thought this and have arguments for almost every scenario. We think we have an answer but wanted to send this out to the community first. I won't post what we are thinking yet, so that the answers can remain unbiased for now and we can have a conversation without it being swayed any one way.

We understand that 301 redirects would be seen as a doorway page. 
We are also only discussing in the context of organic search only. 
If we ran the domains as their own sites, they would be about 3 pages of content only. Pretty static, but good content. Think of a PAS style sales funnel. Problem -> Acknowledgement -> Solution.

[effectdigital]

To me this depends upon the traffic build of your old domains. If they mostly receive direct and referral traffic, then the redirect idea could work very well. If they gain most of their traffic from Google, redirecting them will eventually make them stop ranking as Google don't like to rank (in the long-term) redirecting URLs

Once that occurs, your main site may gain ranking features from your old sites, but even with perfect redirects (using the mighty 301) you would still stand to lose rankings. Google will basically check how similar the last active cache of the redirecting URL is to your new page (the redirect destination). Even with a 301; if the content (in machine / Boolean terms) is highly 'dissimilar', then your new page will only receive a fraction of the SEO / ranking authority of the old (redirecting) URL. This is to stop webmasters buying up authoritative expired domains, redirecting them to themselves and gaining free ranking power

From Google's POV, a lot of ranking 'power' (authority) still comes from links. Which sites have the best links? Do other sites in the same area of the web (same theme) have more quality links? How fresh are those links? Are there any positive / negative trust signals to refract along that axiom?

When a page ranks well on Google, it is because it has recently (or historically) 'impressed the web' (thus gaining backlinks and un-linked citations). If you replace a page which has 'earned' links with another page (like a sales funnel) or redirect it to a completely different page, why should that new page benefit from the same links? The webmasters who linked to the old URL, may not have chosen to link to the new page (be it a replacement or redirect destination) so it shouldn't see loads of SEO authority coming from a past legacy

Obviously if you just change domain and the pages are essentially the same, then it's fair that those pages retain their former Google rankings. This is why Google has to validate the 'similarity' of old vs new pages (whether they replace the current content, or exist at the end of a redirect)

Be careful with your path forwards. You could have a 'great idea' only to lose most of the traffic which those domains were supplying

Obviously if the old domains which you are sweeping up, don't see much traffic from Ads or Google (SEO / organic), then you can do pretty much whatever you want with them. But if the traffic came mostly from Google (organic) then it may be tricky. It may also be tricky to redirect the domains if paid ads are served to them, as ads will often be 'disapproved' if they point to a redirecting URL (true of FaceBook and Google ads). So at the very least there would be a major overhaul of your ads campaign(s) which would be required