Redirecting many relevent niche domain to one

I am trying to redirect my 4 domain (relevant niche) to my main domain. Does it help my main domain rank boost?

I found related discussion about it on MOZ and someone commented there " The risk however, is if the domains have a negative history associated with them. If bad links were pointed at the old domain, then those links will now point at your main site when you redirect them. If an algorithmic action like Penguin or an over-optimization filter was applied to the old site, your risk carrying that baggage to the new site." If this is true then i think anyone can manipulate other/competitor website by simply redirecting spammy domain to their. Confused here....

Dont know, go ahead and 301 all the domains and tell us what happens.

I would love to know.

Common sense tells me you wont face any problems because people spam parasites with hundreds of 301 filled with spam so 4 301's shouldnt be that bad but then again this is 4 full domain 301's so idk.

There are hundreds of pages on old website, should i redirect all of them to home page or manually redirect them to individual page (new domain), The site will retain most of the same topics but many of those old links are no longer relevant to the new site's topics.