I've seen a few debates bout this on some Reddit threads, and even on KVR. Some people swear that plugins add harmonic richness and subtle imperfections reminiscent of analog gear. It seems that every plugin manufacturer (e.g., Waves, Arturia) claims to be closing the gap. I have a Plugin Alliance subscription, and it appears that there are numerous options for "warmth". Do you have a go-to? Is it magic, or just compression, EQ, and fairy dust? Curious about your thoughts on the matter!
I think they add some mojo; how much, I'm unsure. I remember when Waves came out with their BB Tubes plugin; pro mixers were drooling all over it in their ads... it seemed to be malarkey...Greg Wells was acting like the industry and his workflow had changed overnight. As with any plugin, use it if you like the way it sounds and if it improves your mix. A|B and see what it's doing.
Bob