I wouldn't presume to judge my own value to the company, but I might invite the business owners to do so. "I know I'm just a contractor and am easily replaced, but I enjoy the work I do here, and I support the company's mission. If a suitable position ever became available, I hope you'd be willing to consider me, because I'd certainly be interested." Then end the conversation promptly so they don't feel any subtle pressure to comment on your value.
I've noticed that the people who bring the most value to an organization tend to presume the least about themselves.
"It's the best thing since professional golfers on 'ludes." -- Rick Obidiah