It's true there's no way to know that things we try are working, because we lack any kind of true control of all the zillions of factors involved, including the flow of traffic from one time period to the next. The world makes a pretty chaotic laboratory.
But I doubt changing content hurts. Aside from the fact that I update my content regularly and it doesn't SEEM to hurt, I've mentioned before that a website that I filed a DMCA on rewrote all their content - not a sentence was the same, I swear - and continued to surpass me in the rankings to reach and hold the number one spot in the SERPs for a moderately competitive keyword. This was a pretty blatant keyword-domained, MFA site offering pallid value but a nice layout. Changing their content didn't make it surge - it was rising anyway - but the rise never faltered until it got to the top.