Tenure, Unions, and Free Agency

We sat around the lunch table in the English department office today discussing our upcoming Professional Development day. I am hoping to be a part of that experience, presenting about Reinforcing Effort and Providing Recognition. Moving from the topic of that PD, we wondered the reason for all of the PD opportunities this year--we have far more PD scheduled than last year.
I believe that our administrators, from the building level up to the Central Office, are planning to make significant changes among our tenured staff. The truth is that we as a school have not been successful and we need to get better. The administration needs to ensure that we have been given the opportunity to improve our instruction; if we do not, they will then have cause to non-renew. Tenured teachers are of course as nervous as the non-tenured, like me.
As an aside, I am not worried. Not because I think I am the greatest teacher in the world, but because I am confident that my students will succeed in part because of my skill. I am not all that interested in tenure.
This disinterest in tenure seems to bother my union leadership. In the last week alone, I'v been asked twice to join the union. Both times, I have avoided a direct answer. It isn't that I don't value union membership in theory. My previous union had fabulous leadership and effective bargaining skills. Yet, even while they were committed to improving the lives of its membership, I never felt that they sacrificed the students for our desires. I am not as convinced about my current union. Therefore, I don't see myself joining the union.
In the end, I feel a little like a baseball player in a contract year. Meaning, I will be a Free Agent when the summer rolls around. The district will be free to renew my contract or let me walk. It is completely up to them. At the same time, I feel free to entertain other offers, especially the more lucrative ones.
In the final analysis, I hope my performance is deemed worthy. I am willing to take all of the risks that come with avoiding tenure and union membership in hopes that it makes me always strive to earn my next contract.