I'd go with (dry) 'gold leaf' for restoring your item , frogpatch .... there are varieties of so-called gold leaf that have got little-to-no actual gold in them , & those will prob. serve the purpose for that that you seek (and save a big chunka dough too) ; since you'd mentioned that the glass is etched under the existing gilding , putting some leaf (& getting it to 'stick' to the glass) will be much easier than not .
You could polish the glass (with cerium oxide,water & a drop of Dawn dishwash soap) , but too much destruction of the original surface would most likely occur (IMO) .