Jaeger:
From a construction standpoint (and a costs standpoint), it's a no-brainer that renovation is more expensive. That's why I think it is crazy for so many here to talk about architects coming back and making changes over several years. It's just not cost-effective.
From a design standpoint, obviously it depends on what you are trying to do. It's possible to do course renovations even if you have no clue how to route a good golf course, as long as you keep the routing intact and just tinker with the bunkering. But it is very hard to make reasonable routing changes to an existing course, short of blowing it up completely and starting over. Once a routing is in place, there are so many things done which reinforce that routing -- everything from tree planting to circulation patterns to irrigation mainlines -- that there are just 100 things in the way of changing it.