The cost-value of liveaboards varies greatly depending on the location. I've done liveaboards in the Caribbean, Socorro, Red Sea, Maldives, Indonesia, Galapagos.
I generally tip 10%-15% based on quality of service and the value of the liveaboard. A high value experience gets a higher tip %. For example, my Maldives liveaboards were cheaper than Caribbean. Maldives diving blew away the Caribbean. The quality of the boat, food and service in Maldives also far exceeded the Caribbean.
Forgetting about the diving, my tip % in Maldives was much higher than Caribbean because of the value.
I generally tip 10%-15% based on quality of service and the value of the liveaboard. A high value experience gets a higher tip %. For example, my Maldives liveaboards were cheaper than Caribbean. Maldives diving blew away the Caribbean. The quality of the boat, food and service in Maldives also far exceeded the Caribbean.
Forgetting about the diving, my tip % in Maldives was much higher than Caribbean because of the value.