I only recommend sanding when a piece is pretty much worthless due to damage or pitting. If it were something like a Wapak Indian Head or some other prized piece I'd be inclined to leave it be, hold onto it, and hope for a better method to be discovered. If you do decide to sand, do it by hand and you'll be less likely to leave grooves, gouges, swirl marks, and other obvious signs that it was sanded. The marks on your pan don't look very thick. I'd try wet sanding with 80 or 100 grit silicon carbide sandpaper and a small block of wood. Use a small amount of water so a slurry forms. Just enough to keep the surface good and wet. It will minimize the risk of leaving swirl marks. The area you sand will be so shiny it'll look like stainless steel when you're done. Unfortunately it will remain shiny even after manual seasoning. Maybe after sanding you could try dropping it in the e-tank overnight. That should darken it back up although I haven't tried it since I've only ever sanded one piece.