I never replace the rods unless something has broken. I will magnaflux them, replace the bushings, change the bolts and resize them. That is why I use top notch parts. There is no reason to replace them since they don't wear out. I do replace the pistons. The only parts I reuse are the bare connecting rods, bare block and bare heads...plus the accessories. You essentially start all over with a new engine at a small fraction of the price. For example, it is under 20K to freshen up a 75K engine.
I have never had a valve break.....or anything other part for that matter. I error on the side of caution to prevent any failures. I use the best parts I can buy, put it together very carefully, take the time to tune it right, make sure the boat is set up correctly, and rebuild it before anything can get worn out. Hope this helps.