In my limited experience only the Drums or Hindu's add much value. And those are relatively expensive.
The backs are neat to read, as we all know they are the first cards (*I am aware of) that had stats on the back. I see people adding they have a P42, T205 and it just doesn't carry the weight of T206. There are no doubt a few master set collectors going for the backs but not too many. The Broadleafs are of the tougher variety too.
So, generallly speaking, not super important overall, imo
ps....when collecting the gold borders, try to get ones with the least chipping around the borders. There are a ton of T205 collectors on the forum. We have had many discussions over the years.
I sold these when I sold my first collection 9 yrs ago but they give a good representation of some of the backs. I had most of the others but these are some of the toughies. IF doing the set, I wouldn't worry too much about the backs...
