I have written business plans for all manner of industries: a coin operated jukebox company, airlines, travel companies, new product launches, and anti_aging product companies. It is not necessary to have a passion for the product or the company to write or develop a business plan. What you must have is a passion for aggregating information, getting involved with and understanding the service or product, and understanding the financials of the product or service. By financials I am not referring to having a CPA before you undertake the task, but rather understanding the presentation of the information and analysis/ numbers to support the activity being planned. Financials are important because they are the score card in the world of commerce.
Your marketing efforts do not have to be expensive. In many cases, companies that don't have marketing plans spend more than is necessary to reach their customers. With a plan that will spell out the ways you will market your company, you will save money and energy on your business marketing efforts. Creating an effective marketing plan is one of the most crucial elements of planning for your business.