It would be worth studying - if they were much alike, the first obvious questions to answer would be "why" and "which came first".

Worth studying is an interesting term. I've got a bunch of things which are worth fixing, but none of them get prioritised. Would you say that it would be preferable to block the creation of a colony on the basis that it interferes research that might happen one day?

Personally I'd say no.

Didn't mean to imply it; I'm probably the last person on this site to argue against a colony on Mars. But it would be worth it if, during initial construction of the colony and preferably before sending men, we could send over some studies.

I think you've just made a compelling case for why we can make every species on earth extinct, apart from us and 'nothing of value would be lost'.

If that's sarcasm, I think you've exemplified the slippery slope fallacy and the straw-man argument.

Not at all. Your point was that if it is difficult to tell whether a particular organism was of terrestrial or martian origin, it must be so similar to Earth organisms as to be unworthy of study. If so, why bother studying more than one terrestrial organism?