I can see all of your points, but I don't mind answering, and I will continue to keep everyone updated.
It is an interesting question, one that I myself didn't even know immediately how to explain.
First let me make this more confusing. My decision had to do with a feeling, not a decision from the brain. If I had more money, and collected rarities, I would have kept it. But I really don't collect these types of rarities, and am not wealthy enough to really have a collection of them. So after having it certified, my thoughts were to sell it to at least recover the certification cost. Get this...
The certification cost, grading, my postage, and their postage back to me, all added up to over $550.00! But you have to do it to find out what you've got! I was sort of stuck. Why the expertization cost so much, is primarily because their expertization fee is a percentage of the
highest listing of the stamp basically found anywhere. This was Scott's unfortunately highly overinflated price of $10,000.00. (Recent auction results range around one fifth to one third of that).
Now back on topic...
On the other hand...I would certify, and keep an Inverted Jenny (although unlikely to be found in a bag of kiloware). And if I were to get enough for the 554d, I would like to make a play for an unused certified set of the three Graf Zeppelins. Tho, with the 554d's faults, I consider this unlikely for I don't think that it will sell for enough to bring that about. But let's see what happens.
Now, to sum it up, of course each of our individual minds work differently. Mine works in a very "orderly" kind of fashion. There are different kinds of rarities. If it is a rare stamp in my arena of collection I would keep it. But not the EFO type of rarities. Those kind add up to an expensive collection. I would have to have that type of deep pocket EFO rarity collection in order to have kept it. I just felt I could potentially get more for the collection I have by selling it. Out of all of us, I think some would keep it and some would sell it, depending on how they collected.
For example, if I could get the Zeps, that would complete my US airmail collection unused. If not, there are other stamps. And from a practical repulsive kind of standpoint, there are a few things that need to be done around the house. So, I hope for the best, and Pray against the worst.
I'm sorry to have been so wordy, and I hope this makes sense.

-IBFS