This is what I'm piecing together for myself (what I think I know!). I'm inviting others to contribute or correct...
Bonding isn't required to make your pool's electrical system work. There must be 10s of thousands of pools out there that were never bonded. Bonding comes into play when one or more components of your home's electrical system ceases to work properly. If some component of your pool becomes electrically charged, while another does not, and a person touches both at the same time, then that person's body becomes the electrical connection between the two. This could be experienced as a vague tingle, or it could be enough of a difference in electrical potential to cause a very serious shock, even death. If the two components are connected via a big, thick chunk of copper wire (bonded together), then the wire eliminates the difference in electrical potential, and the person's body is not subjected to it.
So, for example, if you bond only the electrical components at the pad, a difference in electrical potential could still exist between pool water and deck. If you manage to bond everything except the deck, same problem. Everything you can manage to bond together is going to be safer, but only if you're touching only those things. The potential for injury still exists while touching whatever you can't bond.
These differences in electrical potential can exist for several reasons when there is no bonding. A gizmo gone bad (or bad from the factory). Bad wiring. A gopher chewing through PVC conduit and encased wiring. A faulty GFI (it happens). Etc. One guy here had an SWG that was putting a small amount of current into his water. It was manufactured with this defect. He could feel it when he touched one side of his pool's decking, but not the other side. His wife and kid could feel it, but he could only feel it if he had a cut on his finger. So two things were wrong: the bonding was not done well enough, and the SWG had a flaw. Maybe you could go forever without ever having a problem. So far you haven't. Or maybe your pool light will spring a leak and somehow energize your pool water. In that scenario, you would have three things wrong. No bond. No GFI on the light. And the worn out pool light gasket.
So having your electrician fix as many things as possible is better than doing nothing. Way better. But unless you fix it all, you'll still have some potential dangers lurking.
And this is where I get a little fuzzy on the subject, so someone else can hopefully corroborate: your house and pool's electrical system could be perfect, but you could still have a problem without bonding because the electrical potential difference could emanate from somewhere else besides your house! What if the same "electrician" that wired your box (the previous "DIY" homeowner, no doubt), went next door to help out his neighbor, and created some other Frankenstein mess next door. So maybe his box is energizing the soil, or the fencing, or whatever. Your neighbor doesn't have a pool, so maybe he's never going to know about this issue. But you do have a pool, and electricity knows no property boundaries!
More doom and gloom. But you get the idea. Start with the panel. Get that cleaned up. Get the proper GFIs installed for your light and pump (I think they're both supposed to be GFI protected). Bond everything at the pad, then start diggin'! Do what you can. You might not have to tear apart all that much concrete. Is there a dirt path between pad and pool? Can you get that far with a bond wire? Can you burry a bond wire around the entire circumference of your pool, in landscaping beds? You can sneak wiring under a concrete walkway, that's pretty easy. Maybe from that ring of wire you can get from there to some of the rebar? Or the pool light housing? Or the skimmer, to bond your water? To be clear, I'm not suggesting how you retrofit the bonding of a pool. I don't know how to do that. I'm just suggesting that, with the help of a qualified pool electrician, where there's a will there's a way, and you might find you have a way...
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