Most brewers go by specific gravity, not bubble frequency.
D-rest won't always be necessary, but I always do one rather than try to detect diacetyl.
I don't do diacetyl rests and have never had a diacetyl problem. I make a cold starter (Stir plate in the fermentation chamber) , pitch at fermentation temp and let the beer sit at 50F for 4 weeks before I lager it. I guess others have different results, because I see a bunch of posts about how a diacetyl rest is always necessary.
Definitely not always necessary to do a d-rest; I do one because I had two d-bomb batches as a rookie brewer (underpitched) and will never risk it again. Sounds like you have your process down pat so keep on doing what works!
Yeah, one of the beers that I consider my best and most consistent beer is a Classic American Pilsner. I have lagered it that way every time and people, including myself, keep coming back for it. If I ever get a D-bomb I that one, I will have to rethink my process.