The business plan contests I`ve researched, offer a fairly small prize - which may not be commensurate with the time and effort involved.
Going through the process can be good experience. However, many have different criteria for selecting a winner than an investor would use. As I`ve told several of our clients, I would participate for the experience and (especially) the contacts - if those connections would be helpful to you and your business.
But, I would continue on your main road to acquiring capital - so if you win it`s like receiving a bonus.