Is a PhD useful if you are interested in a career as a staff researcher, not leader of your own research lab? How useful is a PhD if my final career goals don't involve leading my own research lab?  In a perfect world I would like to end up as a bioinformatics programmer/analyst in a lab or a core facility to help other people with their projects rather than work on my own. (This is what I'm already doing, actually, but I fell into it somewhat by accident, and I'm not sure if I will be able to find similar jobs in the future without a PhD, if I need to leave my current lab. Thus this question.)

Is a PhD going to be a significant advantage for this kind of position, compared to a BS plus equivalent time working in a staff bioinformatics job in academia?  Or are PhDs mostly only useful for people who want to end up as professors or managing research projects in industry?
Looking at your situation, I would say that if you have no intention of teaching and no interest in conducting your own research, a doctorate may not be the best use of your time. It might be better to earn your BS and get some experience under your belt.

That said, a PhD might help open doors in some really cool labs / companies / universities. There may be some jobs that require the terminal degree.