Thank you gents for all the suggestions,
I must say I haven't actually had any problems with the o/e Lucas bullets, spades or connectors, as long as the original connection is not sloppy. Granted at 40 years old they are past their best and the rubber insulation is well past its best. But they are cheap and easily replaced- and at that point one might be more worried about the general health of the wiring loom itself if all were original. They certainly don't seem to suffer the corrosion that Japanese bullets seem to- I'm talking o/e wiring looms on 70s Hondas, etc which can end up an awful rusted and corroded mess.
I read many years ago in an old BSA handbook that BSA abandoned negative earth in the 1930s- because of, wait for it, chassis corrosion. They seemed to be suggesting that positive earth suffered less from this. I'm no electrcikery expert, but this may explain why Brit bikes went to Positive earth- when no one else did!
In any event, a good, waterproof (not to mention oilproof) modern connector seems a sensible upgrade.