46 year old CPA wants to earn reputable doctorate - need advice

Age >40 not a problem

I am a faculty member at a top-50 business school. We would definitely consider candidates who are your age. In fact, your age is something of an advantage in that you would certainly have substantial real-world experience.

... but we train researchers

Your stated primary goal of teaching would definitely be a strike against you. Top PhD programs are primarily in the business of training people who have research as a primary goal. The training we offer is primarily how to create new knowledge, as well as socialization into the institutions of academic research.

I can identify since I went for a "PhD-and-academic-career" after 25 years of a professional career in the private sector (Finance & Administration Director kind of stuff). Although countries are rather different (mine is Greece), we are both in the "western civilization" chunk of humanity so maybe some similarities apply.

What the persons interviewing me for the PhD wanted really to be convinced about, was that I was really serious about pursuing an academic career. In other words "I am doing the PhD for the love of science" (translation in the ears of third parties: I am bored with my life / I have a mid-life crisis /I failed in my current profession etc), wouldn't have cut it. "I want to change course because I very much like scientific research, and I like teaching too), and generally I like engaging in new things" was the correct approach.

And then, even though I had completed a full-time 2-year Master of Science when young, they had me doing it all over again, in order to qualify for the PhD.

I am not sure though about not exploiting your past education and professional experience.

From my economist's point of view (I am a certified accountant also), there is abundant space for important research in linking/bringing together the Accounting and Economics points-of-view on researching the workings of the private sector in the economy.

Or, embarking on a research project combining Management Science and Accounting with a quantitative approach, appears also to be an open field.

It is pretty difficult to provide a specific advice because you probably have pretty tight constraints in terms of time, family, location, etc. My advice would be to spend a lot of time exploring opportunities and weighing different options. PhD at 46 is definitely a good idea if you like teaching. It takes only 3-5 years to get it and it will make you employable long past the retirement age.

My personal opinion is that you should give a lot of weight to a location of the university so you don't have to spend too much time/money traveling as your opportunity costs must be pretty high now.

Also you should analyze the skills that you have and see what kind of research you can apply it to. Being an experienced accountant, you probably have quite a few valuable skills that you can apply to many fields. Going out of field is quite alright as long as you are interested in it and apply the skills you are strong at. For example, my masters was in finance and I ended up doing PhD studying risks in agricultural business. Worked out just fine and of course I went into another field after I got the PhD, applying my new set of skills. Come to think about it, progress is pretty fast so I'll probably end up working on a field that doesn't yet exist later in my career.