Yes, I have had the experience where one "step" so to speak has the power to confer far more than expected change to a rig. In fact I wrote about it and have been using it as I described in my Audio Blast article on Discrete Opamp Rolling the Eastern Electric Minimax DAC Plus.
I call the use of aftermarket discrete Opamps like the DEXA NewClassD or the Burson with the EE DAC a "digital toolkit," which is able to fundamentally alter the source, and thereby the system. I have literally saved the sound of systems costing many tens of thousands by simply rolling discrete Opamps and thereby playing to the strengths of the components.
Do I care if others can't figure out why that can be? No. Do I argue over it? No. People will either accept my advice or not. So be it. The ones who do will discover an exceptionally powerful way to make any system quite appealing to their ears for the grand price of about $1,500 for the DAC and four sets of discrete Opamps.
I disagree, however, with the premise that you can never do too much tinkering. When non-efficacious items outside the signal path are used in a vain attempt to alter the sound, then one has entered the realm of too much tinkering. There are a lot of audiophiles wasting their time and money on ridiculous "tweaks" instead of conducting serious system building, which would move their rig toward a different sound.