I think business plans are great if you are building a business with a known and validated business model (like a coffee shop, restaurant, retail store, etc.) But if you are building a startup (a new business model that has not been executed successfully before), The Lean Startup (http://theleanstartup.com) method or the Business Model Generation (http://businessmodelgeneration.com) approach are better. Steve Blank's resource, The Startup Owner's Manual (http://www.stevenblank.com/startup_index_qty.html) also has some great practical steps.

While, I know you are looking at this as a theoretical educational exercise, I would encourage you to consider taking some of the steps laid out in the resources I mentioned that are practical steps towards building a real business. There is no reason you can't do these things while in school, and you might just end up with something that is valuable.

Speaking from the resume evaluation perspective, I would put more weight on a resume of someone that has done some of the actual work of building a business, rather than someone who did a mental exercise / simulation on a business.

For example:
- Did market research on the perceived need for a new product and the possibility of building a list of potential customers for the theoretical product (not that impressive and / or valuable in my opinion - this is the old school Business Plan style approach to entrepreneurship)

vs.

- Developed a new product design and pitched it to potential customers. Built website and internet marketing campaign for the new product that generated a list of 2500 customer names & email addresses who expressed interested in the product. (this is impressive and is an expression of the Lean Startup)

Here is a great article that describes the different approaches you could take and how great entrepreneurs behave: http://www.inc.com/magazine/20110201/how-great-entrepreneurs-think.html

Entrepreneurship is a hands on exercise. Jump in and go for it.