There are some questions on mathoverflow such as
with answers that tell us things such as:
Mathematicians prefer to use older books because of some old books are full of amazing ideas and some of them are comprehensive (such as books of Spivak).
Question: What older books (with low quality typesetting) would you like to see reprinted with high quality typesetting?
My question is not just a question. We are a group of math students (most of them are geometry students) that want to re-write popular old books using $\mathrm{\LaTeX}$.
One can search for most cited books such as: Curvature and Betti numbers (K Yano, S Bochner) or Einstein manifolds (AL Besse).
Update: We have some rules:
After sending $\LaTeX$ and PDF file of rewritten books to main author or publisher, we delete it from our computer.
We never publish it anywhere on internet (If publisher or author give an answer for re-typing).
We don't want to earn money by selling these books (If publisher or author didn't accept to pay for our work we have no way but creating a donation page after author or publisher approval).