I am not sure what you mean by diminishing returns. My arrows, with four 4" feathers shoot fine out to 50 yds. Actually the longer distance gives the fletch even more time to control the arrow. So distance would work in favor of a small vane. With feathers distance does not appear to have any diminishing returns. I shot blazers and feathers at 50 yds and there was only a 1-3FPS difference. But then I am using a heavy arrow that leaves my bow at 233FPS.

Featehrs won't be quite as durable as plastic vanes but I don't really shoot groups with more than 3 arrows anymore so my feathers hold up pretty well.

If you use tape to fletch your feathers then removing and re-fletching is fairly easy with no real clean up of the shaft. I just wipe it down real well with denatured alcohol.

I have zero issues shooting broadheads with feathers. Maybe my bow doesn't qualify as really fast (IBO rating 307 or so) but no issues.