Definitely some good points and pluses for using feathers. Besides the "vulnerability" to getting feathers wet and the higher cost versus vanes, the only other main reason I see for using vanes is the documented speed loss over distance that occurs with feathers, due to the higher drag they produce (which is why they stabilize arrows so well). Archery Report ran a pretty extensive test in 2010 of several vanes and at least one set of feathers, measuring arrow speed up close, at 20, 30 and 40 yards, then graphed them all so the reader could see how each performed. You can read the report here (http://archeryreport.com/2009/10/fle...ew-speed-drop/). 4" Gateway feathers were tested alongside several vanes from different makers. In the "speed" test, at point blank range, the feathers were the fastest out of the bow, but they also slowed down the fastest over distance, falling to the middle of the pack of tested vanes at 30 yards distance. By 40 yards they were at or near the bottom of the slowest fletchings and ended up with the greatest drop overall. This report also tested the noise that each one produced and it was noted the feathers produced the most noise as well, again to be expected given the high amount of drag they produce in flight.
While the Bi-Delta vanes I use weren't included in these tests, I have used Blazer and 2" Fusion vanes, which were tested, for quite some time. In calm conditions all three of these perform so close as to be hard to discern any real difference, even out to 60-70 yards. It was when I tested all three in windy conditions that I discovered, at least for my setup, that my choice of 2.5" Sharkstooth vanes outperformed Blazer and Fusion vanes as the Sharkstooth fletched arrows were hitting/grouping very noticeably closer to my aiming point (i.e., less wind drift) out to at least 50 yards, which was as far as I shot in those windy conditions. Again, these are my observations with these three vanes and with my setup. Your mileage might vary but I thought I'd throw this out there for others to read and ponder.
2008 Martin Firecat Pro-X (29" DL, 66# DW), home-made TRG, new VEMs, DS Advantage/HHA Pro-5519 front sight, No-Peep Sight Eliminator, Limb-Driver arrow rest, B-Stinger stabilizer/dampener, custom upper STS, G5 Head-Loc quiver on custom mounting bracket. Gold Tip Velocity XT300 arrows with Bi-Delta 2.5" Sharkstooth vanes and Grizzly single-bevel broadheads, 498 grains at 262 fps (22% FOC)