Strategic planning without strategic thinking is essentially impossible. In fact, the notion of developing a strategic, or long-range, mission-identifying plan, absent thought processes highly attuned to such an exercise would be something of a non sequitor.
Inasmuch as the concept of strategic planning requires the ability to think in broad, long-range terms about the direction in which an organization should move and the environment in which it operates, you really can't have the plan without the thought. Consequently, top officials within a organization will seek to surround themselves with individual who do possess the ability to think strategically. Any business that hopes to remain in business for a long time has to have employees, or know where to find them, who can make long-range assessments of how the market or external environment will change over time, and what internal transitions must be implemented to prepare for that future. Strategic planning involves making assessments of what part of an organization is well-suited to anticipate market changes or changes in the competitive environment and what parts are likely to become functionally obsolete. A department or division identified with the latter category can be expected to be eliminated if it does not itself demonstrate the capacity to adapt.
Strategic planning, and strategic thought, involve a willingness to view skeptically one's position in the world, and to plan for how to transform oneself so as to avoid one's demise. It involves constant attention to external developments or trends, and to environmental and regulatory factors that can influence how it conducts business. All of this requires "strategic thinking."