Dataviz is nearly useless for tweaking something like indirect illumination cache, as a lot more than just a sample distribution needs to be observed (sample color, variance, interpolation, leaks, light bouncing, etc...). This quantum thing does not make sense either... you can simply enable the mode that changes HD cache ONLY when HDcache is set as primary GI, and revert to correct HDcache as soon as it is not set to primary mode.
Sorry, but there is simply no excuse for not having that option there....