If the engine is apart its best to do the bearings. The only way to truly examine them is to remove them from the engine, put a side load on the bearing and turn it with your finger to see if its notchy, but for the price of a set from RC Bearings.com if you're going to do that you might as well throw them out and replace them.

Vibration won't make your plug go bad.

Running too lean, using RTV for a muffler gasket, and a bearing coming apart will make your plug go bad.

As for the RTV, if you use a very thin smear where none oozes out into the exhaust flange, you're fine, most people tend to over do it and it WILL snuff your plug immediately if if flecks off and gets back into the combustion chamber, this is well documented.