most panel beaters should be able to sharpen them. atleast thats the only place ive heard of. but yeah they arent really easy to sharpen. hence why i gave up on them

i either do as i described above, if i dont need the panel that im cutting out...as its a very destructive process. and i usually only do it when there are not that many spot welds

or i get a die grinder with a rounded head on it and just die grind the spot welded section away

but yeah the spot weld drill bits work well when they are new, but as soon as that centre bit gets blunt they just get annoying