No Ach doesn't lower 'IQ' it induces some depressive symptoms (problems assimilating and conentration) and with chronic raised levels it will tank serotonin (and by extention melatonin - causing insomnia), raise noradrenaline causing anxiety, hypervigulance and lower dopamine causing decreased hedonic tone. Obviously you are unlikely to have a gross increase in Ach across the entire brain in a mental illness and this is why supplements are less likely to cause all of these effects. The decrease in those types of neurons firing will only be in certain pathways that are effected by Ach ex: Mesolimbic and Mesocortical pathways (pleasure, motivation etc) which have very little to do with memory and learning functions per se (although they provide the motivation the excitation to other areas). These symptoms aren't the result of 'low dopamine' - which has very little directly to do with learning.
The only half reasonable way I can think of to lower Ach is TCA therapy.
Yes he is absolutely right, but on average, having acetylcholine on the higher end of the range is a good thing - but you are right, it will do nothing for short-term memory, but it does play a role in releasing neurotrophic factors and potentiating long-term memory and good memory consolidation. However, it seems the link here is individualized receptor based calcium channel modulation, and because the hippocampus which is largely involved with spatial memory, it would be expected that low acetylcholine individuals would have trouble remembering directions and where they put their keys etc...
I also know that low ach levels are associated with more aggressive mindsets, but because of a totally different reason than what high ach would bring . Low AcH tends to create overstimulation just like high levels...but I would mirror high levels to be more like that of glutamate excess (racing mind etc) - whereas too low would be almost purely adrenaline like....the difference you might ask?
Say you go for a walk - and someone pisses you off or sais something you don't like - low ach levels would make it so you wouldn't even think of it and you would probably react really quickly, almost in a tourette's like fashion...whereas high levels of ach you would probably be more cunning and pre-meditated.
At the same time though, even with being naturally undermotivated, high ach individuals tend to have more long-term goals and as such generally refrain from violence.
So if I were to choose from the two, high ach would be better because I could always tone dopamine on necessary points, but most preferably...having a balanced level of the two ....which would be moderate dopamine for common sense and logic, and moderate to high ach for more complex tasks and remembering what is necessary...then you also need glutamate for detail oriented things, and attention to details and philosophical thinking.