If the Euro was not in so many difficulties, he would have used that. Indeed, it's not legally obvious that you can secede from the UK, but join the EU without accepting the Euro as mandated for new members.
He's a republican (small R in these electoral times), but once he establishes the right to decide the Head of State (and Queen Elizabeth dies, leaving the much less popular Charles to take the, uh, reigns) he can fight that battle in the future. No point making it part of this particular war.
First establish the principle, then push for its conclusions. No one ever thought Salmond was anything other than a shrewd operator.