Yes, there will be a time when design changes are incremental...

Yes, there will be a time when design changes are incremental and size increases no longer yield cost or efficiency gains. After that, it will be reduction in manufacturing costs that will be the make or break. Same with wind turbines, Li-ion batteries, Silicon solar panels and so on - design and size are fairly stable, but costs have reduced dramatically as manufacturing volumes have increased. Markets and governments have show patience with these technologies, and hopefully will do the same with wave power.