An interesting thought game might be to imagine yourself as part of an intelligent but hitherto unknown (to 40K) alien civilisation. You suddenly have a God's Eye view of the galaxy and in depth details and history of all its other major civilisations. You're then told that it is completely inevitable and unavoidable that you will be discovered by one of the other civilisations / species in the galaxy and that you have the power to pick which one, but you DON'T have the power to change their more usual approach to dealing with aliens.
Looking at your species in in relation to the Tau, the Imperium, the Eldar and indeed any other race / civilisation, which would you prefer to be discovered by and why? You're not permitted to have suicidal tendencies or want a 'quick death'.
Your goals are survival first (so the largest number of your people not being dead), followed by quality of life (so readily accessible food and water supplies, a place to live in security, the freedom to raise a family, gainful employment of some sort, that sort of thing) followed by maintenance of your culture (so keeping your civilisation - language, norms, customs, ideologies etc - as close to how they were originally as possible).
In response to an issue raised further down in this thread, I'm adding the following proviso:
you also have to imagine that your planet / civilisation has something that all the other truly factions want or need.