If there is one thing I have zero knowledge of, it is the spa services. I do know it is a major revenue center on any ship, and a sales pitch is skillfully given during an initial service in hopes of garnering more business. It isn't high pressure sales - from what I've heard - and the massages seem to be highly rated.
The spa on the Holiday is quite limited. These things weren't a huge deal when the ship was built, not like today when the spas cover a large area.
Hey - it's a cruise. I'd go for it.