I have found that being personally interested in the product has a lot of benefits. First, if you're a user/consumer, it's easier to determine which features are most important as well as usability issues. It's surprising how unusable some products are because the developers never actually use them.

Second, and most important, a personal connection helps to get you through the dark days at the start. It's very emotionally draining to work on something that has no traction, no supporters, and just a bunch of naysayers. If you love the product, though, it can offset this emotional drain quite a bit.

In my case, I built a tabletop gaming (ie. DnD) CMS. In the beginning, nobody used it except me, and it was tough to go upstairs and hack away every night and weekend. However, I used it and that was enough to keep me moving. Now, we've got thousands of users and paying customers, and the motivation is much easier to find. But, I never would have made it this far if I didn't care so much about the domain.

Unfortunately for me, I think there's probably a lot more money to be made in "boring" areas. If you can keep motivated to work on a CRM or medical billing system, you'll probably end up making way more than my DnD website. But, it will definitely be harder to keep the momentum in the beginning.