It is your house and you can do ANYTHING you want with it. I would do whatever makes you the most comfortable and gives you the most enjoyment and practical use out of the space you have. If I were in your position I wouldn't hesitate for a nano second about making the master bedroom a sewing room...in fact, I'd have to ask you what's taking so long!
Go for it. From what you've said I doubt that you would regret it for a minute. It sounds like it would do nothing but enrich your life and what's more important than that? Good luck with your decision!