G'day Gary, someone more knowledgeable in this area can probably answer the triangular tail question more adequately than me, but I was under the impression it's a float for lure action purposes.
Regarding other add-ons though, I have tied fly material onto singles and trebles at the back end of my lures, with some success, and this has 2 benefits: (a) it helps stabilise the action of the lure a bit, acting like a mini drogue in the water, and (b) it also adds some flash and sparkle to the tail end of the lure. I am now just speculating, but I wonder if some flash on the tail hook also helps if there are toothy critters around, to encourage tail bites which in turn minimizes the chance of the entire lure getting snipped off (there's also a chance I might be talking completely out of my a###, and tying fly material on the back hook makes no difference whatsoever
).
Cheers
Angus