Many people think there's something wrong about being spiritual and having wealth, especially making money from offering spiritual advice. I don't know if it's because of the history of monks and priests taking vows of poverty. I don't know if it's because money is connected with business, and that is a decidedly unspiritual place. I know I have had feelings that it was unseemly when someone became quite rich from spiritual writings.
But is that perspective grounded in a spiritual truth? Money is considered bad by spiritual people because it is often obtained through unethical behavior, corruption, exploitation, etc. People who crave money will do almost anything to obtain money.
Also money obtained is often put to use in very unspiritual ways . . . conspicuous consumption, gainer power over others, flaunting oneself.
These very statements, however, make clear that it is not money pre se that is tainted, it is the things that people will do to obtain money and how they use it. Money is not the root of all evil, it is our culture's obsession with money that is the root of all evil.
Therefore, there is nothing inherently wrong with making money through spiritual products or services, or being spiritual and making lots of money. The important point is that one does not do what you do as a way of solving the problem: how to make money. One does this out of love and responsibility and devotion, and yes, secondarily, to bring in money. Second, that if you do obtain wealth, after taking care of your reasonable needs, you use it to benefit others.
The other point to remember is that in our society, people, even those spirituality-minded, listen to those who are acknowledged leaders, who have that power. In the spiritual realm, unless you're a monk, the only source of that kind of esteem is evidence that your product sells, is valued by others. So doing well financially is actually critically important to one's efforts to share the dharma and make a difference in people's lives.
Therefore, for people who see themselves as having a spiritual purpose, such as myself, it is imperative that they be sufficiently successful at it that people are drawn to read their books and partake of their services.