This was not my topic to begin with, so I am not sure exactly what preserving value meant to the original person. To me, I interpret it as buying a card at a market value and then trying to help maintain that value, or the perception of that value, even if it meant overpaying for something you already had.
If you tried to do that with mid 90s inserts for example, you might find mixed results. Many people have dumped formally great cards at bargain prices in the 2000s to recoup whatever they could in a softening market, however sellers like Burbank Sportscards holds firm, often at what many consider to be inflated prices. I'm sure they are successful often enough to make it worth while, as they are obviously losing on volume sales due to a policy of setting higher pricing to capture the best possible individual sales.
I found myself doing this many times in the past, bidding up Garvey cards I already had. Not minding if I won, but really more wanting the card to sell at a range closer to what I paid for mine. If I won, great. If I lost, the buyer was not getting a bargain at least. I didn't see it as wrong, nor do I now, as long as it's not my items I am bidding up (shilling).
Now, to the cornering the market comment. Are you saying if jaderock (for example) buys all 8 copies of the Fabric of the Game card at market rates, this may be illegal if he intends to resell them? Even if he intended to buy all of them, demand is only so great for an individual player and he may not even be able to make his original investment back. However, if anyone in the marketplace had a chance to buy any one of the copies when they sold originally, how is him outbidding all takers wrong, even if he plans to resell them and thinks he can make a profit by doing it? Chances are he won't make a profit if he was always high bidder, but it could happen.
The funny part about this topic is that on the other site, it seemed quite a few people frowned upon this type of activity! If you weren't buying it purely to own it because you wanted it, it was bad to push up the price!