Space operas were popular even before the Second World War.I don't see there being space hero shows in the 50s and 60s like Buck Rogers and Star Trek. The German rocket program and the Cold War accelerated spaceflight so much sooner than made any economic sense - and, more to the point, got everyone interested in space as a matter of national pride/staying ahead of the commies in the arms race - that people wouldn't have got excited about space exploration then. What takes their place on TV, other than more sitcoms?
I think nothing would have changed, except that most likely not space battles would have been popular, but travel and adventures on the alien planets themselves. For example, as in the Martian epic Burroughs.