My two cents on the subject?
Go for the Diploma and then you can have your employer pay for the additional schooling as you want or need it, and it will not be out of your pocket.
Go for what your gut is telling you to do. I have a Diploma in Nursing and an MBA, as well as a BS, and it has never stopped what I have wanted to do in any way, shape, or form.
Best of luck to you.