I do open old blisters (and new), but I let most stuff be inside untill I am 100% the stuff will get paint on them.
There is more reasons for this, since I don't buy things I don't intend to paint eventually. But over the years I have ended up opening lot of boxes/blisters of things that never got any paint and was sold in the end, this mostly apply to new miniatures though.
So why don't I rip open the old stuff? To be honest I am not really sure, since I can hold the blister or packageing and really want to open it and see the miniature inside, but I just can't do it anymore. Actually I feel less hard about old Citadel stuff, since even the rare old stuff is not really so rare. But when I have old lead from really strange and dead companies I sometime wonder if there is any other unopened packages out there and it might just be a real loss forever.
I am deffinately in the hobby to paint and game, I just think I am getting stranger as I get older.