The makers of Effetto Mariposa Caronga tape say that the rim should be completely clean for the best bond between the tire and the rim. Other makers may have different recommendations, but tape will always stick best on a smooth and clean surface.
A new layer of glue will soften the old glue, but the adhesive in the tape won't do that, or at least not nearly as well.
If you intend to use tape I would recommend that you clean the old glue off, I would avoid using a wire brush to remove the old glue. I had very good results using the Effetto rim cleaner - you could not tell that a tubular had ever been glued on the rim.
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Dale, NL4T