So an update. Over the weekend I installed new grips (Avon Contours) and did the zip tie mod. My Volusia had aftermarket grips on it that were 1.65" in diameter and I had heated covers on top of that making them like 1.75" total. These were too big for my hands, so I went with Avon's 1.45" grips, making them 1.55" total. Surprising thing: the Avon grip's throttle cam was already slightly larger than the previous set. This was minimal, but just something to note.
After getting everything else set up (Avon comes with two cams, one for Honda, one for other Japanese brands, and you need to glue the cam on first), I cut a zip tie of appropriate size and glued it on with superglue one section at a time. The cables already will hold it with tension, the glue is there just to prevent it from sliding side to side. Took some time as I did about 0.25" at a time, moving from one end to the other and letting the glue cure. The end result was that the radius of the throttle cam was larger by about 0.1" or so. Once installed, this resulted in reduction from roughly a quarter turn to 1/5 turn from closed to WOT.
I took it for a couple of drives. Around town the bike gets into the power band just that much easier. It does not feel jumpy at all, just results in a smooth transition from idle to power band. The difference is small but noticeable and pleasant. I also did about 60 miles on the highway last night going between 60 and 88. Here the difference is a bit more pronounced. I can cruise at 65 on a flat straight stretch just off idle in 5th which is nice, but the biggest difference is that when I needed to pass four busses in a row I could hold my wrist in a much more comfortable position to get to the peak of the powerband. With the old setup my wrist would be at a silly angle, requiring me to either just suffer that or turn the throttle, then hold it in place with my palm while moving my hand further up and then turning it some more. I am happy with this mod, though if I ever do it again, I'd probably add a next size up zip tie to get the angle from 70 degrees to more like 65.
Overall, so far I am glad I did this. It also makes me wonder why so few manufacturers make progressive cams to keep the rpm uneven but the torque curve flatter. Avon can clearly ship two cams, why not two dozen with different profiles. For a high revving bike you could get a cam that gets from idle to 5,000 rpm quickly but then gives you more room from 5,000-15,000. For a long stroke V-twin it could be the opposite: slow ramp up in the first half of the cam, followed by a quicker ramp up at the high end. In either case, I am glad I did this mod that cost me a total of $45 for new grips and $0.25 in glue (the zip tie didn't even cost me a penny since it was a cut off end).