When beginning to approach investors it is absolutely necessary to have eliminated all of the possible risks that may be associated with their potential investment. What I mean by that is each step you take along the process all the way up to a firm user base or customers purchasing your product eliminates risk from an investors point of view. The business plan is just the first step and assuming this is your first version of it, as you develop your product and begin to "beta" test, it will change more than you probably even realize at this point.
In my experience, the process should be something like this (assuming you have $0 to personally invest):
Stage 1 - Concept/Business Plan with investors consisting of family, friends, self and a company valuation of $250K - $1 million
Stage 2 - Technology is developed with investors consisting of Angels or Seed VC's. The company valuation can be set from $1 million - $5 million
Stage 3 - Launch of product & early customer traction with investors consisting of Seed VC's or a Series A VC. Company valuation set from $5 million - $10 million.
Stage 4 - Scaling & adoption (company has negative cash flow) with investors consisting of Series A/B/C VC's. Company Valuation has huge variability at this point and can be valued anywhere between $15 million - $100 million.
Stage 5 - Rapid & Mass Expansion (positive cash flow). This stage will usually involve an IPO or Exit Strategy Implementation. Obviously the valuation of the company has huge variability at this point.
All of these stages represent a removal in the level of risk involved with an investment into your company.
I would suggest using this initial business plan as a frame of reference for your ideas. It should be used to keep you and your partners on track. If your main concern is that you will be beaten to the market then completing what you view as a flawless business plan will only hold you back. Begin product development and if possible complete it as well.
From an investor standpoint, people have incredible ideas all of the time. The hard part lies in executing the technology and implementation of those ideas into the market. If you can eliminate as much risk as possible, not only will you find it easier to locate potential investors, but your valuation will obviously increase and the cost of equity will increase substantially for the investor.
I hope this helps!