If you do get forced into sanding, just take it down to epoxy. (not glass) Wet sand it to make sure no blush was there. Do a trial patch of varnish first. You can use it for a while with no varnish. How long was the varnish on there before these pimples started showing up? Most epoxy becomes inert once it has out gassed fully and is totally cleaned of any blush, which is necessary before any topcoats are put on. This is why I swear by wet sanding the epoxy before varnishing. Although yours was cured for quite a while, did you scrub it good with soap and water before varnishing etc.?