For those of you who have purchased Zeta, was it worth the additional cost to upgrade? What are the biggest advantages to going from BeOS 5.03 Pro to Zeta. I'm trying to cost justify the $99.00 cost. Should I wait for the next release?

Well, it is only worth the cost if you need applications to run or maybe devices to support.
Zeta has bone network stack so you will see many apps at bebits that require bone/zeta. You could get by for the most part with pro. It will not cost less. You can try it though. There is a live demo cd out there for zeta. It doesn't work on my laptop so using the demo saved me money. You might find that you would like it.