All my 800K floppies seem to still work without error. That said, I'm not going around storing important documents on them either. At this point I assume that any of them can fail at any time. The good news is that most old software is available on the internet. If you're worried about particular applications or documents you have on the disks, though - I'd find a way to back them up.
As far as the capacitors, all you can really do is power on the machine and see if things work. If it works, great! I'd only worry about it if the machine stops working, and deal with it then. A failed capacitor won't hurt anything else, and I doubt you're using the Plus for any mission critical work. 😉