To me it sounds like you're actually proposing 2 seperate mechanisms to play a part in this enhanced vividness of dreams.

1- The repeating of impressions during wake life in dreams..especially the last impression of the day.

2- Extra awareness during dreamstates due to some earthly obligation.

The first one i think (but not know) is only the case when the impression was intens, or long enough..so quantity or quality..like looking at a shocking picture before going to sleep, or playing a full day of hypnotic guitar heroes.

The second one is where i think it becomes interesting.
I've done a lot of "research / googling / whatever" about addiction.
Like sex and food, risk is a dopamine release trigger as well. This is why for example the first time coke was most probably the best. Coke blocks dopamine reuptake, and risk produces more dopamine.
The more times you take coke, the less risk/reward there is.
This is also why gambling is addicting. people are addicted to the dopamine release that gets triggered by the uncirtainty of a reward.

Anyway,..what i'm trying to say is that these people cant fantasize themselves in a way that they physically produce the same effects as a first timer,
so i dont think this can be expected to be achieved by creating a fake fear screnario either.

However..that does not mean that your theory is flawed, ..i Do think you're on to something.. days with high expectations Do make me dream a lot more intense than normal days.
I think that the way to make it work, is to create some type of russian roulette situation..
a device that can potentially desturb you, and your neighbours (social responsability is a high attention trigger)..for example..have an alarmclock set to 'wake the neighbours' and let it randomly go off somewhere within a week with a programmable timer..
although that suggestion might be a bit hard to realise for some,
i think the Key of what im trying to say is that the situation or expectation that you create (the open door) Must be real...there Must be a real chance of it happening..whatever it is.