I'm not sure what the current W satin finish is.
In the past, it was fairly "rough", almost textured as it was applied, and in places where your body rubbed it (like your hand on the back of the neck) it would just buff out to a nice luster. In that luster, you could clearly see the grain.
If you want a smooth gloss finish on the headstock, you'll want to knock down the existing satin finish "level". You can use some 400 paper on a sanding block for this.
Once you get it to that point - look at it.
Since you're painting it... the superglue fill, and re-level is an easy way to go. Spread it on thin with your finger tip, let it dry, level (with the block please). You'd use some 320 paper to level the super glue, then 400 or even 600 to get a nice smooth base for the paint.
I mean, you're gonna have to evaluate whats there, as you go, and modify accordingly. Spike, Jack, Me... nobody... can say for certain, as we dont have the wood in hand, and we dont know how the finish is exactly, and what you're planning on doing exactly. You do. Ultimately, its yours.
But we're here to help!~
PICTURES!~ please