I recently replaced the manufacture's polyfill with MUNDORF MSilence TWARON Angel Hair and MUNDORF MSilence TWARON Unicorn's Tail speaker cabinet filler in all the 5 chambers of my 5 way speakers.
Also worth mentioning was the chambers were filled about 20% more quantity wise than as shipped by manufacturer.

Results:

The improvements in sound stage in the tweeter and higher midrange housing were the least (if at all). But in the lower mid-range and most definitely the bass output improvement was palpable - more natural, less bloat with more defined but more importantly it seems to me I am hearing lower bass frequencies. I have not done the measurements with my dB meter yet, will get back when done.

Form this experience, I would say do not waste your time and money doing the higher ranges but for the lower ranges it is money and time well spent doing this easy upgrade.