My fiberglass bathtub has several small cracks that have just developed, and I am wondering if there is a repair that can be done other than a tub liner or replacing the tub altogether

We have a fiberglass repair man that pops in once in a while. He will be able to answer your question... But based on his previous responses, yes, cracks in fiberglass tubs can be repaired...

You might check out; fiberglass repair - Google Search
Or check the Yellow Pages for a repair service. Good luck, Tom