You have no doubt used the intercom function more than I have, but my experience was a little different.
- Voice activation is slower than I would like, but in my experience it only took 3-4 seconds at most. Still probably not fast enough to warn of gravel in a corner, or to inform a passenger of that cute bunnyrabbit on the side of the road ;-)
- The radio hiss when the intercom is active doesn't seem nearly as loud as you described, and is the same in voice-activated or always-on modes. Is it possible your wife's mic was picking up some wind noise and transmitting it to you?
- I had a passenger who couldn't deal with the delay in voice-activated mode (she would start talking but forget to wait for the link to activate, then push the button and disconnect herself), so we used always-on mode sort of like push-to-talk: hit the button to activate, push it again when done conversing.