Warning light.

It really depends on what DTCs have been logged, and whether they point to changing the plugs as a solution.

Without knowing what codes have been logged, you are just groping around in the dark. It is better not to be guessing.

 

There are many different things that can cause warning lights to come on. I wouldn't advise driving it unless I knew what was going on with it. Is your 12V battery low, or do you have a way to check it?
Can you see the fluid swirling inside the inverter coolant reservoir?
Have you tried disconnecting the 12V ground cable to clear the warning lights and see if they come back on immediately?
The best thing to do is either take it to have the codes checked by a dealership or someone with Toyota specific scanner, or buy something like the mini VCI and do it yourself.

 

I saw your thread title and thought "Yeah, right!" Then noticed you were a Kiwi. Welcome!

You don't say where in NZ you actually are, is there a Toyota shop or an independent Prius shop close?

If you think it needs a set of plugs, by all means do so. I'm suspecting that that won't clear you code. But after you do the tune up, clear the codes by d/c'ing the starter battery and see if they come back. While you're at it, check everything you can under the hood (bonnet) to make sure it's not low on lubes and that the inverter coolant pump is working.

Can't advise you on whether its safe to drive it. I'm still new at all this. But I think I read if the check engine light isn't flashing, it isn't urgent and is not a 'do not drive' issue. But it's your car, free advise is worth what you pay for it. I suppose I'd be talking to a Prius shop for advice about whether you can drive it in for a scan.