Is There Evidence That Supports That There Is A Return On Investment for Strategic Planning?
One challenge with this question is that it's very hard to show a causal relationship between any one thing a company does, and positive effects, because real world life is quite complex. The best we can get to with these kinds of questions is to look to see if there is suggestive evidence.
There is some suggestive evidence
Watson Wyatt undertook a study to examine whether companies companies whose employees understand the company's mission and goals produced superior returns as compared to companies where this was not the case. Their conclusion was that when employees understand the company role and mission, there is a 29 percent greater return compared to other firms (Watson Wyatt Work Study).
If you believe that employees will be more productive if they see that their work has meaning, and understand how their individual contributions "make a difference", this finding is not surprising. It really does make sense.
There's another interesting point, though. In another study (Workplace 2000 Employee Insight Survey) it was found that 75% of employees did not believe their companies actually did business according to their stated roles and missions.
What that says is that a lot of strategic planning (and particularly related to implementation) fails badly in terms of actually guiding an organization, probably because the plans are often ignored in real corporate day-to-day life.
And, of course, badly executed plans aren't going to positively affect any company's bottom line.