To what extent will a spirit based stain affect glue adhesion I wonder? Varnishes, oils, absolutely, oil based stains, for sure, they are bound to compromise glue strength, but with a spirit stain that just distributes microscopic dye into the wood and evaporates then I wonder. But there are so many stain types and so many adhesives that any attempt to generalise is futile. Even if Dirtystains red dye was fine Dirtystains blue might not be, and by the time you've done tests to be sure...

I would scrape a heel with a Stanley knife blade rather than sanding, I think I'd do better at keeping it flat like that.