A good article in the January-February 2014 Harvard Business Review highlights the challenges of strategic planning.
Detailed plans may make managers feel good but too often they matter little to performance. Strategy is about being uncomfortable, taking risks and facing the unknown. There are three simple rules:
Keep it simple - summarize in a One Page Plan
Don't look for perfection - Strategy is not about finding answers. It is about placing bets and shortening the odds.
Make the logic explicit - Be clear about what must change for you to achieve your strategic goal.
The Mindshop process of facilitated Strategic Plans needs only ten or twelve pages headed by a One Page Plan.
The key is in implementation.
Many benefit by having external discipline from a facilitator and mentor.