I think there are some interesting thoughts you brought up. And I want to tell you my experiences – from my personal point of view, of course:
There are different ways to find inspiration for a new composition. Just to mention the two most common for me:
I’m diving into my libraries of sounds and synths, having lots of fun and being fascinated by all the varieties and possibilities they offer. It is really like diving … being completely lost in sound and bliss and hardly getting my head over the surface. 😉 And sometimes – yes: only sometimes – the idea for a new song is a direct result of a patch I just detected. Or a sound that leads from one chord to another and to a new composition.
The best way for me for writing a new song is to go back to my basics: the piano. I have a handful of pianos that I prefer to play when I want to write something new:
– my Rhodes (yes, the real thing)
– NI Alicias Keys
– Waves Electric Grand 80 piano
– and two or three more, depends on my mood.
The piano is everything you need for composition. (If I was a guitarist I’m sure the guitar would be my weapon of choice, of course.)
It can be quiet, slim, with only a few notes. Or it can be an orchestra. I miss nothing.
When I found the core of the new song, the idea and the structure, I go back diving into sounds. To find the best arrangement for the new song, the best environment of sound. And sometimes my basic piano track is just the “pilot track” for everything that comes next and doesn’t even appear in the final mix.
Also I don’t think we all sound the same just because we have some Spitfire or NI or whatever libraries. I’m sure most of us have thousands of sounds available and can hardly ever use them all. (Tipp: Never use a patch or a pattern “as is”, always change something to your very special needs and taste.)