Funny thing about my experience with 'tweaks' (which I consider to be outboard stuff which are add on's, not primary equipment such as cables, interconnects, etc). I could most always hear a change but, as time passed, not so much. I eventually forgot to reinstall them when changing stuff and am presently using only one. A Loki tone control to help tune some upper mid range glare in CD's, etc. Sort of turned into an agnostic about this issue.
Three-easy-payments, fundamentally I agree with you, and, IMHO, much of the 'tweaks' controversy is driven by folks with financial interest.