I'm following this thread for over a year now and decided to finally register, as I can provide some info and personal experience on this question.
Short answer: Yes and no.
From the thread history it seems that it depends on people's own preference (as everything regarding sound). Throughout the posts a general consensus was reached that the Gallo aplifier was more necessary with ref 3.0 and 3.1 speakers, as they're a bit harder to run.
When I bought the ref 3.5 speakers I powered them with an anemic NAD D3020 amplifier which was originally used for running Divas and TR2 woofer. As this amplifier had only 30 Wpc@8 ohms, it produced virtually no bass. When I bought the speakers I also got the Gallo amplifier in the price, so I used it to power the secondary voice coil. The amplifier crossover was tuned by ear to a high 150 Hz to achieve a flat response in combination with the D3020. This pairing worked perfectly well for both music (which I listen a lot) and movies. The bass response was linear to about 35 Hz and audible above 20 Hz. I haven't heard the speakers with two separate subwoofers to comment on such integration, but I was utterly impressed with the stereo bass when film effects asked for left-right interchangeable explosions.
After about a year, the Gallos were too much for the D3020 and burned the amplifier's output stage. Thanks to Gallo amplifier's versatility, for the last 9 months I use it to power the main speaker connectors, with the secondary connectors disconnected/open. The bass response is linear to about 60 Hz, but I do miss the extra bit. Even in music (I listen to mostly classical and jazz) the bass sounds a bit "thin". It is present, but not in the previous fullness.
Long answer: Depends on your current amplifier(s) and sonic preference.
Anthony usually (always?) demoed the speakers with a pair of high powered monoblocks (I think about 500 Wpc@8 ohms) and without the secondary coils powered, so the Gallo amplifier isn't necessary for representative sound. I haven't heard them yet amplified like that, so I can't comment on the sound. If you have the chance to try the amplifier out, you should definitely do it. Only you can tell does it make a significant difference to your ear or not.
Hope this helps!