So - are you are suggesting that - if it is not 'salvation', it is 'non-essential'...? Or, are you saying that 'non-essential' doctrine is what "separates" believers into denominations...?
All doctrine is essential - as being part of the truth of scripture - which we should all endeavor to correctly and properly understand and follow.
However, at the same time, I can agree that believers may "agree to disagree agreeably" about "certain things" for the sake of fellowship - what those "certain things" are depend on the context - two believers [from different churches/denominations] who work together on their jobs or meet in a public place in town, two members of this website discussing something in a thread, two members of the same local new testament church together in a worship service or some other activity of the church - or, any other context - it actually makes a difference. We might all agree that it should not be any different from context to context; nonetheless, in reality, it really does make a difference. And, in each of these contexts, the two believers will have to be in agreement about what is-and-is-not essential for the sake of fellowship in that particular context.