David MacKay's "Sustainable Energy - without the hot air" [1] does a good job of putting energy sources like this in perspective. Wave energy is indeed challenged by issues with mechanical parts; however, the reality is that there isn't much wave energy their to begin with. As MacKay puts it, "sun makes wind and wind makes waves" [2]. Waves are just diluted sunshine. Sandia National Labs does a good job of putting this into perspective, assessing solar electricity with a theoretical potential of 89,000 TW and ocean wave with 34 TW [3].
We could try to make the case that, despite the small potential, wave power is convenient to extract. We do this for hydropower, for example. However, where there are waves, there is wind. On cost and reliability, I don't see wave power ever being able to beat out offshore wind.
1. http://www.withouthotair.com/