I think the Biggest mistake people make is asking, "does it work" about any marketing strategy!
The question itself begs for an anecdotal answer that is completely irrelevant to your circumstances...
More importantly, the amount of people who have given up on strategies too soon or because it wasnt done in a way to provide empirical evidence, is staggering... and the amount of misinformation that flows out into the wild built on those flawed premises is really problematic for those without the context of your situation and the relative context of the situation where those opinions were formed.
The second problem is that opportunity cost is rarely measured by marketers. The third problem is that your resource allocation relative to your objectives is arguably more important than any other factor or opinion about a strategy.
Marketing decisions should be made in the context of your resources, goals, and your broader marketing mix.
The idea that you can evaluate a specific strategy and measure its return in a Silo without considering the opportunity costs and other available strategies relative to your specific resource limitations is very dangerous and needs to be killed off!
The ideal scenario is to optimize to cashflow relative to lifetime value and time value of money...or get as close as possible to this...and choose strategies within the context of this calculation.
You want an SEO strategy? First, figure out if your audience is there and the cost to reach them with paid search and how long it takes to turn into cashflow and the lifetime value of that customer...than evaluate the costs to optimize to rank for that keyword, and how long it will take, than look at your other resources and strategies relative to the likely costs and returns and time to get cash returned relative to those strategies and decide if its worth investing in ranking there...
Once you identify a proven keyword and have context for the cost and value and time and oppirtunity costs, than figure out how to rank for that keyword... maybe you buy a site that is already ranking. Maybe you advertise on sites already ranking. Maybe you think about the user and find a way to create a resource that Google will want to rank because of its utility... and than create empirical tests to measure progress and than you invest !!!
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The shortcut SEO strategy i like is to ask yourself, what resource can I create for my industry that is not online but would offer so much utility that google has no choice but to optimize their algorithms to rank my resource... like wayne gretzky, go where the puck will be in the future...
When is SEO is done right, its Google trying to optimize its algorithms to rank your content, not vice versa!
Just my two cents.