Outbreeding is only helpful to the extent that it's a deterrent against severe inbreeding. The returns on outbreeding diminish very quickly.
i.e. unless you were planning on knocking up your sister or cousin if not for your different-race squeeze, it's not going to be any better than knocking up Jane-next-door.
A relatively high inbreeding rate can expose populations to a greater degree of recessive diseases, like Ashkenazi Jews; and severe inbreeding can nick away at traits like height and IQ. However, as we see with Ashkenazi Jews, their level of inbreeding certainly does not preclude maintaining a high average population IQ.
So if you're from a relatively inbred population like Ashkenazis, maybe having kids with someone from a population like gentile whites can help some with recessive diseases--but it'll likely result in kids of lower average IQ than if you'd kept it Ashkenazi--obviously, this effect would be even more dire with a population with lower average IQs than gentile whites, and no additional value-add on recessive diseases.
If you're from a reasonably non-inbred (the "races" are reasonably non-inbred), relatively high IQ population and have kids with someone from a different, but lower IQ population for the goal of having "better" kids, that would be like cutting your nose off to spite your face.
Substitute IQ for whatever other traits or combination of traits you might care for.
Furthermore, there's regression to the mean. Even if you know Sloot 1 and Sloot 2 have identical IQs, the offspring of Sloot 1 will be lower in IQ than that of Sloot 2, on average, if Sloot 1 is from a lower IQ population.
"Mixed" people, on average, come out in between their parents--just like "non-mixed" people.
"Race-mixed" Latin Americans (and not all Latin Americans are substantially "race-mixed") and Central Asians certainly show no signs of "hybrid vigor" with respect to IQ--whether "hybrid vigor" being out-performance on a given trait vis a vis the average of the parent populations, or the out-performance of the higher of the two parent populations. Generally laymen mean the latter, like ligers where male lions and female tigers tend to have very large offspring.
My future kids (or at least some of them
) will likely be quite mixed, but not for any "hybrid vigor" reasons. Just the pattern of girls I've historically been banging...