Hmmmm, not 100% sure from what you've said. Sites or subdirectories?

Sometimes, the corporate side of the business wants its own presence away from specific products, and that's much clearer to define. In that instance, i'd probably suggest using different domains.
eg.
corporate site .whatever
product site1 . whatever
product site2 . whatever

There is no hard and fast rule for this because every business is different.

Hi engine, I think the issue is that at the moment the website does not particularly show excellence in any of its areas of focus because there is too much distraction. Creating a site or directory of only core competences may allow us the focus to show that we do excel at this core activity. And the second area would include the array of other business which we have and want to continue to have and continue to grow.

From an SEO POV I wonder if both the core site and other site might perform better because of greater focus and more harmony in things like key words used across the two sets of pages?

I know a lot of larger companies do this sort of thing, for example that they have domain/en/ or domain/de/ for different languages and some massive companies like GE have business1.ge.com and business2.ge.com etc

It sounds like you're doing something similar to what I did about 15 years ago; since then, I've set up about 60 domains that look and feel independent, but are really showing data from maindomain.com/seconddomain.

Meaning, you go to foo.com and it looks like foo.com, but you're really seeing data from bar.com/foo

I've had advantages and disadvantages over the years... advantage being easier to maintain than 60 separate websites, disadvantage being that marketing each site is a lot more expensive. I'm also not sure that Google was happy with what I did, as my ranking has dropped to nearly non-existent when I used to be #1 or #2 on virtually any relevant keyword search.

I've been going through a major rebuild, and the plan is to more or less undo what I've done and redirect everyone back to the main site. So now, when you go to foo.com, you'll be 301 redirected to bar.com/foo

Hi csdude55 and thanks for your post. I am leaning towards just having domain/ab/site and domain/cd/site because we only have one brand name that is already meaningfull to clients and the market more widely. Then we would have what looked like two separate sites which shared a family resemblance and plenty of cross site links.

I am assuming that we might still be able to do this with one WordPress dbase?

That's how I WISH that I had done things, I would have saved a lot of money on marketing. Running it as multiple sites is basically running multiple businesses.

My sites are ad-driven, too, and I'm convinced that a single site with 20 million monthly pageviews will be worth more than 60 sites with 20 million pageviews spread out.

But by merging them now, I risk a lot of backlash from Google, so I might have a really bad year while trying to get everything back to a single site. I reeeeally wish I had just done it like that in the first place.

As for Wordpress, I have very little experience with it so I can't help there :-(

Hi again csdude55, I don't expect any volumes of sessions anything like that, we are very niche. But if we can make one online entity more fully show that we are expert in our core area, while the other entity shows our other areas off well, it might make sense to make it work.

I have a feeling splitting out the contents for entity 1 versus entity 2 is going to be some work - and we will have all new urls which will mean going back to square 1 with g organic. Hopefully the new sites may recover in time organically, I am not sure how long that might be though.