I find this variety interesting and very undervalued. I think the market will climb on these as we are seeing a surge of collecting interest in the past couple years.
An interesting bit of info is that the legendary 3 legged buffalo is also often found with 2 1/2 feathers. The 2 1/2 feather variety as was stated before is indeed a result of over polishing / abraiding the dies in an effort to remove clash marks, It just so happens that this is the same cause of the 3 Legged buffalo and have you noticed the prices on them? I think its just a matter of time before more people become savy to these gems. Also if you take the time to look through dealers stock you can still cherrypick these varieties as they are often overlooked and un-attributed.