I have never used tape, but as far as I know tape can be used alone or with glue.
Needing to remove the existing glue depends on its condition. That being said, every time I have glued a rim that was new to me I have cleaned it down to the rim then started from scratch. If I am working with a rim I have glued in the past and the base layer of glue is in good condition I will leave it.
If you were gluing you can leave the existing glue in place.
If you are going to use tape you must remove the existing glue. I have used Effetto Mariposa Carogna Tubular Tape Remover before. Took a good few days of applying, leaving to soak, removing residue, cleaning and then repeating the process. Not quick or easy but got down the to the rim bed and left it like it was new.
So giving I have no point of reference as to what “good glue” looks like, the glue on there looks to me like any glue that has had the surfaces separated. i.e its patchy. Should I give it a wipe down with some Acetone to smooth it out or just apply another layer of glue when I am pre gluing the tires?