At CoasterMania '92 the keynote speaker was Cedar Point's director of maintenance and construction. At that time he revealed that through their normal maintenance, it takes approximately three years to completely re-track the Blue Streak. In other words, none of the track on Blue Streak is more than about three years old. I think the structure lasts a bit longer than that, but each board is replaced as needed.
At the end of last season, I noticed a large quantity of lumber stacked up beneath the Gemini. A couple of years ago, quite a lot of the structure was replaced over near the mid-course brake; apparently other sections of the ride are being replaced this year. My guess is that unless we look closely we probably won't notice the change.
The wood structure on coasters faces something that the wood structure of your house does not: wear. Boards rub against each other and the bolt-holes egg out because the structure shifts under the massive loads of the coaster trains. I don't know for certain, but I am guessing this is why the park is replacing structural lumber on Gemini.
--Dave Althoff, Jr.