Ok this is interesting… I had a client who has several domains like around 12 redirecting to the main website (different URLs) and I didn’t see any problem with that…
40 seems a BIG number to me and it can show a red flag to Google… keeping the Mikes idea in mind why not divide the domains…
Out of 40 domains let’s say use 5 for industry related blog and update them one a month with some quick link building on it.
Other 3 as QnA websites… mostly it will be a UGC data so it won’t increase too much of your work…
Redirect 5 websites on different URLs of the main website….
Use the next 2 domains on a review website… again a UGC so not much work in a long term…
(use c class IPs)
… and the same way divide the domain pointing from one website to different others and optimize them to get traffic from them as well…. Why I think it will be interesting is because it will take you to the safe place and at the same time you will be opening several different channels to attract qualified and targeted traffic to the website…