Prior to the flyby of the Mariner 2 robot probe in late 1962,
some scientists had predicted Venus would be everything from
a steaming jungle with dinosaur-like creatures slithering through
it, to a world covered in crude oil or seltzer.

Note if you watch the introduction to George Pal's 1953 classic
SF film, The War of the Worlds, all the planets in the Sol system
are given brief inspections EXCEPT for Venus, which gets no
mention at all, not even a glimpse of speculative artwork by
the great Chesley Bonestell. Because in 1953, life on Venus
was still thought to be as possible as it was on Mars - perhaps
even moreso acccording to some lines of thought.

Note 2: In the original 1897 novel, H. G. Wells had his Martians
heading to Venus after their failed attempt to conquer Earth,
where Wells speculated that the second planet from Sol might
have life that wouldn't foil their plans.

Even if Venus were nothing more than "just" a desert with 300 F
temperatures under a perpetually cloudy sky, I don't know how
any of this could be appealing to would-be explorers. They could
not take off their pressure suits and hauling back resources would
be seriously expensive. Maybe watching seltzer or oil oceans lap
against the transparent colony domes would somehow be of
comfort and interest to those who settled there? Or maybe a
lush tropical jungle with exotic plants and the occasional lizard
peering in at the new neighbors.

And couldn't you just see the brave men of the colony heading
out into the jungle to hunt giant and deadly Venusian dinosaurs
with their laser rifles for something to do on those incredibly long
afternoons?

I guess anything would be more appealing than a dead desert
where only dust storms come to "life" once in a while.

About Carl Sagan advocating the changing shaded regions on Mars,
he was actually one of the first to decide that the changes were
due to Martian dust being moved around as seasons changed on
the Red Planet, not plant life. You can read this in the 1966 issue
of the Time-Life Science book, Planets, where Sagan was science
consultant. That book also has some nice visual depictions of the
various old views of Venus.

It is ironic, considering how much otherwise Sagan was such an advocate
for Martian life while everyone else demoted Martian life down to some
struggling microbes by the time of Viking. Here was one time Sagan went
with the facts rather than his fondest dream, as he once said.

As for the Galilean satellites being disappointments, I definitely can't agree
there. At best, most astronomers thought Jupiter's major moons would be
like what we eventually found most of the Uranian moons to be: Ice balls
covered with craters. Sagan did go so far as to suspect that Io might have
some sulfur in its craters to explain its bright colors detected by the Pioneer
probes, but that was about it from the normally conservative professionals.

Instead, we found a moon with nearly a dozen active volcanoes, another
world covered in cracked ice with a deep global ocean (and life??), and
a third moon bigger than Mercury, which turned out to have a magnetic
field, a likely active core, and perhaps a sub-surface ocean as well.

Titan has actually done the reverse of the other worlds in terms of how
the scientists of the pre-Space Age thought about it. Bonestell gave
Titan just enough air to make its sky a deep blue, but that was about it.
Instead we've got an orange ball with a nitrogen atmosphere and air
pressure not terribly higher than Earth's. And the surface - a bizarre
kind of Earth, perhaps. As for life... man do we need to really explore
that place! One blurry surface image just isn't enough.

At least we have all those exoplanets out there to let our artistic imaginations
go wild upon... for now.