If you're just going for maximum gelatin extraction, pressure cookers are the way to go. Much faster and easier than doing it on the stovetop, and the results are often preferable.
Vegetables should only be added to stock or broth (or whatever) toward the very end of the process. After an hour or so, their vibrant aromatics become muddy and dull. I pressure cook roasted bones/meat alone and then simmer aromatics for 30 minutes once the pressure comes down and I have the lid off.
Adding vinegar doesn't really do anything to help with extraction. There have been a lot of bogus theories proffered about doing it, but adding a small amount of vinegar isn't going to appreciably shift the pH of a pot of stock. People like Sally Fallon and the Weston A Price foundation used to recommend adding vinegar to help extract minerals from bones, but then someone pointed out that bone broth doesn't really contain much in the way of minerals regardless of how it's prepared. Cooking bones for a long time or under pressure will convert a lot of collagen into gelatin, yes, but the vinegar isn't doing anything to contribute to that result.
