I've been working through http://www.greenteapress.com/thinkbayes/ and am quite enjoying it. My only complaint is that he, as intended, teaches using programs and a computer and I learn better by doing stuff by hand. He also has a think stats book at http://www.greenteapress.com/thinkstats/ which people might find interesting.
In pure math, since H. Lebesgue in about 1900, the usual good theory of area is Lebesgue's measure theory. The ordinary ideas of area we learned in grade school, plane geometry, and calculus are all special cases. But Lebesgue's theory of area handles some bizarre, pathological, extreme cases. And we can show that there can be no really perfect theory of area -- e.g., there have to be some bizarre subsets of the real line to which no nice theory of area can assign a length. But, once we have the Lebesgue theory, the usual way to show that there is a subset of the real line without an area uses the axiom of choice.
Well, in 1933, A. Kolmogorov wrote a paper showing how Lebesgue's theory of area would make a solid foundation for probability, and that approach is the standard one for advanced work in probability, statistics, and stochastic processes.
a) lots of people do have an intuition for Venn diagrams. Just look at the number of Venn diagram gags on xkcd.
b) it is a great mental image to have if you move on to measure theoretic probability.
There is a book “Probability and Statistics for Engineers and Scienctists” by Raymond Walpole. That book is excellent. Rolling dice and pulling colored marbles from jars is how you teach probability.