The whole idea that [if you don't remember something then for the purposes of decision making it didn't happen] seems fundamentally ridiculous to me. Actually it's wierder than "didn't happen" in this example, it's "as if it was not about to happen" because you will have forgotten it some time in the future. It seems even more bizzare to me that you suggest leaving this in tact and instead resolving the paradox by changing the way you accumulate utilons. All this suggests to me that when accounting for memory failures you can't always correctly judge the best decision from anywhere other than an entirely external viewpoint. The fact that this is difficult to actually do is just another one of life's challenges.
I actually think poor decision making as a result of overly discounting future costs works both ways. People under-value in hindsight the amount of effort they put into getting something once they have it. Imagine for instance asking someone on a tropical holiday whether it was worth working all those extra shifts to save up for it, they're bound to say yes. If they went on the holiday first and you ask them while they're working a bunch of extra shifts to pay the bill you might get a different answer. The bias as I see it is to overvalue the present and discount both the future and the past.
So I don't really see why we should assume our future self knows any better than the present or past versions. They just have a different bias. What we need is a "timeless" version of ourself...
So I have a conundrum. Imagine that Omega comes to you and offers you two choices:
First choice: You get a moment of moderate pain, let's say a slap and then another slap, so that your face hurts for a couple of minutes with some anguish. Now after that pain has faded and you still have the memory of it, Omega measures your discomfort and gives you exactly the amount of money that gives enough joy to compensate the pain and then a cent. By construction, the utility of this choice is one cent.
Second choice: Omega inflicts on you hell for a finite amount of time. Your worst fears all come true, you are unable to distinguish between reality and this hell, the most painful sensations you will experience. After this finite amount of time is over, Omega deletes all memory of it and gives you essentially unlimited monetary funds but still, this experience does not quite compensate for the previously experienced hell if you would remember it. By construction, the expected value of this choice is negative.[1]
If we go by expected value, the first choice is obviously better. Of course Omega forces you to take one choice or you will just get hell forever, we want our thought experiment to work. But if we go by the decision procedure to choose the option in which our future self will feel best, the second choice seems better. I have not yet found a satisfying solution to this apparent paradox. Essentially, how does a rational actor deal with discomfort to get to a pleasurable experience?
[1] I realize that this might be a weak point of my argument. Do we just simply add up positive and negative utilons to get our expected value? Or do we already take into consideration the process of forgetting the pain? Maybe therein lies a solution to this paradox.