Walt-- The $275k appraisal was last year, the $365k appraisal was within the last couple weeks. Not far apart, timewise. IMO, the $275k is in line with what *I* think the house is worth, the $365k is in line with current market values (RE market here is exploding, and I'm in a high-demand neighbourhood). I don't expect values to collapse anytime soon, given the factors that make my location valuable.
I highly agree that I need a plan, and shouldn't just borrow because it's available.
Celery-- Mortgage payment would go up from ~$1100 to ~$1600. I am fully aware that I won't be getting all this capital for free. I have always been extremely careful not to overleverage myself, so highly doubt I'm going to throw caution to the wind now. If I do go through with a cash-out this large, I intend to do so with a plan and reasonably diligent research beforehand. It's just that I can make plans that are potentially 4x as big as I was thinking before, and there are more possibilities open to me than were before, when I only had $10-20k to work with.