I wanted to get to this. I know you've shared this sentiment before, but as much as I can understand the idea and desire for buffs, not nerfs, I think this concept is terrible within its own merit.
Think of what this mentality would induce: By buffing up a card, yes we would see it more often in play. However, this may lead to it overpowering the other alternatives, making previous cards the new obsolete. For those obsolete cards to come into play would require those to then be buffed; but than other cards aren't seeing play. With all these cards getting buffed, they might even begin competing with higher mana cards, which would then have to be buffed. So on and so forth and actual power creep would be surging through the cards.
Now this is extreme and one sided, but this does illustrate a real issue about the effects of a buff mentality. By utilizing both buffs and nerfs, proper power distribution can be (ideally) achieved and managed, which (in my perspective) would allow as many cards as possible to be viable for use.
2 thoughts/examples I've had lately relate to this topic perfectly.
Blood Tear Alchemist - 1 mana - 1/1 - keeps effect
Swamp Entangler - 1 mana - 1/2 - provoke
By nerfing BTA and buffing swamp entangler assists in creating the possibility of actually seeing more variety of 1 mana minions. Obviously, this approach could be used across the board, but these two have come to mind for me lately.