这（个）是我的，this is mine: Before 是，normally I would omit 个 这没有道理, this doesn't make sense: Before 有 I would find 个 strange. Although maybe that is because 有道理 is an abstract concept. If I was talking about which car has gas, I would say 这辆有汽油, not omitting the measure word. 这个在我房间里：This one is in my room: I would find it strange to omit 这 before 在.
So what's going on here? I have an intuitive sense (which I think is correct, but maybe it's not) about when the measure word can or should be omitted after specifiers. But I can't find a unifying theory that explains it.