I know the Red Shell spyware was removed, but I need to know if the game still tries to install any other potentially unwanted programs, or software that isn't part of the game itself.

I also need to know if the game still tries to spy on you — collect usage data and phone home with it.
And, if so, whether or not the game will still work properly if the phone-home attempts are blocked by a firewall or by disconnecting the Internet connection.

Thank you

It doesn't install any third-party spyware now, but Unity still has analytics, which KSP uses to monitor it users. The game works properly even without an active internet connection; my desktop PC isn't connected to the internet.

Thanks very much for the response. The information you provided — combined with the fact that the game is (as of writng this) 75% off — is enough motivation for me to finally purchase the game.
I'll be monitoring its behavior during and after installation. If I find anything additional worth reporting, I'll report it here.
Thanks again :)

No problem! The game's certainly worth it (though i'm not sure about the DLCs) if you're into this kind of stuff and 75% off it's a great deal.

Independent SQUAD versions of the game (up to and including 1.3.1) would ask if the user wants to allow Unity analytics. I think Take2 published versions (1.4.0 and up) might not ask and just gather it anyway.

Some folks have assembled a huge list of dubious domains that can be blocked by adding them to the operating system's hosts file, which you might be interested in. There's a section called [unity3d.com] (including brackets) which lists the blocked Unity analytics domains.

https://github.com/StevenBlack/hosts