The old building next to the zoo was smaller, so it was more cozy and you were just surrounded by fascinating things. And it had a periscope. It might well just be nostalgia that remembers it as a superior experience, however. I share the fond memories, but it's hard to say the new location is objectively worse. It's a lot larger and spread out, for sure, which changes the ambiance significantly. But it accommodates a lot more people. And there's an actual submarine now, instead of just a periscope.
Also, the museum store was not just a gift shop but a real science supply center. You could buy lab supplies and chemicals. I recall it was a lot cheaper than buying from Fisher or Sigma-Aldrich. They even had a branch store down in Eugene.
I am not sure what was special back in the 70's (I only started going int he 80's) but they were in a different building near the zoo back then. When the new building was built they had to pay for it with increased ticket costs.