speaker capacitors-----leave alone or does it open pandora's box ?

Those red ones are Audyn Q4 capacitors. I replaced them in my tube preamp with the Audyn Cap Plus  - white and much larger, and the improvement was significant. True Coppers are supposed to be better for certain applications but they have a very long break-in period, especially larger values. Not tried them in speakers. I've also tried Jantzen Z-superior capacitors in a couple of speakers and one other tube preamp and I personally found them more balanced than the Audyns and take less time to even out. I was also told by a couple of (tube) preamp designers/manufacturers that if switching brands when upgrading capacitors you may need to adjust the values to get the improved sound quality. Others with more experience can chime in.  

^^^^^ You ask a question I've also been wondering about. The tube preamp that I modified cost under $1K new and the cost of the capacitor upgrade was under $70 and took me under an hour to do. It would have probably been cheaper for the original builder buying them bulk. The sound improvement was significant. I don't get it either...