The problem with measuring CI effectiveness is not that it's complicated. It's that anyone notices. At least in the work cultures I was a part of in corporate America, there is usually a "more important" organization which needs to take credit for something that benefited very directly from CI - and does so.
BUT, in the end, you simply have to carefully log what you uniquely accomplish and contribute to and make the case regularly and without fanfare. Specifically, you provide an early warning system to what competition is going to do which enables your org to react more quickly and be right more often because of the rigor time affords. You save your company tons of money by providing insights into better ways to do things (benchmarking) thereby enabling them to stop doing it the wrong way sooner. You are a key inputter to process improvement based on others you know who have "been there, done that". You help your organization get to market much more quickly and efficiently. When you know what competition is doing, it tends to focus response much more quickly vs. doing infinite scenario analysis that ties up far more resources. By uniquely articulating competitor's rationale for R&D choices, you also shape product development and innovation. Etc.
When you get it right, you build sales and market share and margin - and enter new businesses/relationships. It's that simple. And, you make sure your org does it more successfully more often. It's really no different than individuals on other successful teams who make individual claims built on team or organization success.