Other areas to collect
You also might decide to collect what you think is GOING to be popular in 20-30 years. That's a great way to ensure long term success and view your collection as more of a investment versus just a hobby. They're alot of people who decide to sell an entire collection once it's complete if there’s an actual and definite end or what they've accumulated over 40-50 years of collecting. Both ways are very profitable.
You might also decide to collect a spin-off of cookbooks such as Homemaking or Housekeeping books of the past. These are also great sources of information and invaluable tips about every problem you can imagine. These books are the original sources of "old wives tales" which of recently you’ll find more people are turning to for alternative remedies. There’s also parenting, family and vintage crafting books that have become extremely popular as of recently.
There is focusing on the kitchen as a whole, usually narrowing it down to a certain decade or era but then collecting utensils, bowls, equipment and maybe decorating examples.
Vintage Cookbooks are for everyone who has ever wanted to bake something special and turned to a modern cookbook and realized they never seem to have all the ingredients at the same time, there're for history lovers that want to feel connected to the past in a way that's missing in history books, there're for the people that love that musty old book smell and laugh at kindle's, they're for people that feel like we as a society have gone a little too far, a tad off course with life and want to get back to the simple and the real, and they're for the people that want to pay homage to all the grandma's and great aunts that did it best!