The issue is I don't think that settles the original question at all. The wording of the card is different enough, although similar, that the case changes...
Discarding cards and "spending clues" don't have the same meaning although their effects of "losing X of something you have" may have the same outcome.
To put it more into a more rules based answer:
Each investigator discards one card...
Okay, we go around the table and players 1, 2, and 3 do it, as per the rules of resolving effects and order. Then player 4 says, "I have no cards". The game state changed. Done.
Spend two clues...
The player says, "I only have 1 clue", then you don't have what you need to initiate the resolving of the effect. The game state didn't change.. you need to do the other option.
I get the similarities, but it is distinct enough to not be covered by the case above.
Of course, in the other thread I said, and stick to it, that this "spend two clues" card is probably poorly designed and won't exist... but it is more of a theoretical argument than anything.
To twist it in another direction...
What about Offer of Power: https://arkhamdb.com/card/01178
Revelation - You must either (choose one): draw 2 cards and place 2 doom on the current agenda (this effect can cause the current agenda to advance), or take 2 horror.
If you are one doom away from flipping the agenda, can you draw 2 cards, place the first doom (which flips the agenda) and then do you place the second doom? Or do both dooms get placed simultaneously? This is probably closer in line with the original question, but I'd say you do what it says and place both dooms, then the agenda flips. Leaving you with a fresh agenda with no doom.