Corners are a funny thing. We had "bent corners" which were actually bent, rounded that were really fuzzy and rounded, and then good corners which were pretty good although not perfect but we didn't care. The card shops would sell cards that were 6-8 but only trade for cards, at half book mind you, that were absolutely perfect. In those days cards came out of packs in pretty good condition. Every once in a while you would get a miscut card, wax stain, gum stain or a bashed in corner but old cards sorta got a pass. These days you get packs with peeling foil board, miscut (my 2008 heroes baseball boxes still pisses me off, two boxes worth of basecards 85/15 or worse and no real way to replace them), crappy corners etc.
We all know that vintage cards get huge premiums at psa 7 (sometimes) and higher, but the question is does it really matter. On close insepection of the card, you can certainly tell, but a PSA 4 and higher can have a ton of eye appeal. Unless you are an obssessive compulsive a PSA 5 (BVG 5.5?) can meet your needs and save you a ton of cash. Plus nobody is going to say your collection sucks when you have this in your collection:
Just thought I would throw in a PSA 9 for comparison. A superior condition card in every way, but I would rather have all the stars from the 51 bowman set than 1 PSA 68 Topps All Star. Now the pay off
PSA 5 Spahn $80
PSA 6 $128
PSA 7 $150
PSA 9 Harmon All Star $140-$170