I'm reasonably sure that high IQ (i.e. over 140) is not particularly well correlated with outstanding achievement. I am almost certain that extremely high IQ's are not a prerequisite for extraordinary achievement, though there may be some specific fields where this does not hold true (say, theoretical physics).
If someone with an IQ of 180 has a thousand times the chance of making some incredible breakthrough compared to someone with an IQ of 140, shifting from 1% of the people having IQ > 140 to having 25%+ of the people having an IQ over 140 would still probably generate a great deal of breakthroughs.
There is one study that demonstrated that among top 1% SAT scorers investigated some years after testing, the upper quartile produces about twice the number of patents as the lower one (and about 6 times the average, if I remember right). That seems to imply that having more really top performers might produce more useful goods even if the vast majority of them never invent anything great.
Even a tiny shift upwards of everybody's IQ has a pretty impressive multiplicative effect at the high end.
Interpersonal skills are more important for job success than IQ...
There was some talk here about height taxes, but there's a better solution - redefine shortness as a treatable condition and use HGH to cure it. They even got FDA on board with that, at least for 1.2% shortest people.
Unsatisfactory sexual performance became a treatable condition with Viagra. Depression and hyperactivity became treatable conditions with SSRIs. Being ugly is already almost considered a treatable condition, at least one can get that impression from cosmetic surgery ads. Being overweight is universally considered an illness, even though we don't have too many effective treatment options (surgery is unpopular, and effective drugs like fen-phen and ECA are not officially prescribed any more). If we ever figure out how to increase IQ, you can be certain low IQ will be considered a treatable condition too. Almost everything undesirable gets redefined as an illness as soon as an effective way to fix it is developed.
I welcome these changes. Yes, redefining large parts of normal human variability as illness is a lie, but if that's what society needs to work around its taboos against human enhancement, so be it.