Estonian expat Ernsy Opik showed Mars should be pretty heavily cratered long before the space-probes, yet few people listened. IMHO the disappointment of Mars is what made the Space Program so easy to kill after "Apollo". Venus had already faded as an easy target by then.

Back in the late 1950s Venus, as now understood, was being revealed by spectroscope and radio observations. Most astronomers knew it was a hot, hot desert by about 1955, so Mariner 2, in 1962, only confirmed general opinion. Even Arthur Clarke's one Venus exploration story, "Before Eden" (1960), mentioned a hot surface at 500 F or so. Of course the early estimates of 250-300 C were off by 150-200 degrees, but the idea was right. No one AFAIK forsaw the clouds would be sulfuric acid...