Can't really disagree with the above, alien visitors are going to be either an advance group probing to see if we should be enslaved or eaten or obliterated, or the first arrival of the main horde who will enslave or eat or obliterate us.
Best case scenario, we end up as an addition to some coalition whose chief just wants more seats on the intergalactic council and once they've got those we will be 'accidentally' mis-filed for enslavement or 'accidentally' mis-labelled as food, or 'accidentally' used as target practice.
Tricky questions about timing and timescales are easily avoided by ancient/alien tech being found by archaeologists.
(a favourite episode in a certain show, titled 'wormhole x-treme' captures this brilliantly with a tangle of conspiracy within conspiracy)
So much fiction would be nothing without conspiracy. Flights of fancy are better without all the questions - take a hint of a conspiracy and make it the origin for any story you like, and as an idea it easily sticks... alien crash site in Antarctica, change the name from Byrd to Witwicky and voilà your film franchise is... transformed...
And the idea lives to see another day.