I've bought plenty of 70's but if I have multiple issues of the coin or commemorative -- like my National Park series Saint-Gaudens "coins" -- I'm very happy for the 69's. Many times I see asking prices (and actual prices) being 100% more for the 70's over the 69's.
It's been my limited experience that MS 70's have always brought more where I shop around at, but that's not say If I see a coin (same coin) that's more dollars for a 69 than a 70 raises a flag to me, to investigate further to see why? except for high collectible or rare excluded.
Nobody can spot the difference between a 69 and a 70 with the naked eye. Friends don't let friends buy ms-70