Phd, yes the "less is more" is they way to go if you have a well sorted system.
But if there is a problem area that needs to be fixed, then by adding the right preamp that can tame or accentuate that problem area, then yes by adding the preamp that has those colourations in that area then it can be a pseudo fix.
Good luck on finding the right preamp, as they all sound different, in different areas.
Audio enthusiasts, reviewers, and even manufactures have allways said as far as I can remember, "the prefect preamp" should sound "like a straight wire with gain" which funnily enough is the direct in approach with no preamp.
But I'm of the school that looks at the problem area and changing to or modding the component that causing it, not by adding another one into the signal path chain to gloss it over.
Cheers George