I have ONE cake recipe I don't make with butter, and that doesn't have eggs, either, it uses mayonnaise. I mostly make muffins with oil, they keep better, butter-made muffins go stale noticeably faster.
Your reasons for using oil are perfectly sensible, but butter is too yummy for me to do without.
I can taste the difference, and I'll always pick real butter, unless there's a really good reason not to.