Spot weld cutters are about the only way to remove most of those type panels without wrecking the sheetmetal around it. RPITA when there are a lot of them though. About the only other alternative I know of is to chop out the whole area then replace it with new metal. Under some circumstances, not a bad option if you have the metal working tools & skills.
BTW...I HATE spot welds. They just about always leave gaps between the two sheets that trap moisture. Thank goodness I only had a couple to deal with on my '46.