One definite common ground
Math and Physics.... but that isnt really an ethos... Of course the interpretation of physical laws would differ- for instance the implications of quantum physics can be viewed in many ways.
Personally, I believe there is other intelligent species in the universe, but I doubt we will ever communicate with them- that depresses me a little... Personally I think the Fermi Paradox is far more significant than an 'interesting question'- there are two possible answers....
1) Intelligence is _extremely_ rare, ie it has only happened once in our galaxy of 400 billion stars and we are it....
2) something that is done on the way to spacefaring causes the end of the spacefaring race...