really? they seem more likely to be neutral than anything? also sometimes must be good for example children of older fathers are taller
And actually, hybridization between near species or more robust mixing between more genetically unrelated pairs tends to be better for more useful adaptations.
Unfortunately we already killed off, or out bred all other members of genus homo. Though to be fair our ancestors do seem to have got on with them so maybe we just absorbed them more than drove them to extinction?
But in any case, increasing the mutation rate, does increase the chance of bad mutations of happening, since it increases any kind of mutations from happening.
Exposing yourself to excessive radiation is much more likely to cause cancer than superpowers. (In addition to a bunch of neutral mutations that do neither.)