I guess it depends on what you mean by inspiration. If I have inspiration that means I’m already writing even if its in my head; I have some little spark of an idea already. Sometimes we feel the drive to create but struggle to find inspiration that leads to that spark.
So if I am really feeling inspired to write, at least with the way I approach writing, it doesn’t really matter if my playing is rusty or whatever. Inspiration is fleeting so I’m just focused on grabbing hold of it and getting what I can from it before its gone. Once I have that idea recorded or worked through enough to not forget it I can work on it from there for however long it takes.
For some things that will be more vocal/melody focused and I figure that melody and the basics of the guitar parts in tandem and let them kind of work off each other and then you start to get more of a “big picture.”
But what’s paramount is that whatever it was that came from that strong inspiration that made you feel something, you get it while its there. Whether it was a riff, a beat, a melody, a lyric, whatever.