I kinda assume the main obstacle is biology, the main difference between this planet and another planet exactly like it, is that there has been no contact between the 2 over their entire history.
for the most part aliens coming here, we going there, it doesn't matter, if you can't integrate or adapt to the conditions and somehow make yourself immune to the alien diseases viruses and bacteria, your not gunna get very far anyway.
if you imagine the planet as a body, that works well within its self contained system, taken the full 3-4 billion years to attain that synergy, and then you throw a foreign body into the mix. it will just get attacked by every microscopic germ there is of which they very well may not have developed an immunity to. for all we know even something like the common cold could be devastating to an alien race. but in the end its all hypothetical, getting past the biology barrier, integrating yourself with alien flora and fauna isn't going to happen instantaneously.