I think we must make things clear, paper look and feel, tone transition(density curve), granularity(fine or coarse grain), tone neutrality(gray shift), resolution(details), they have different meaning and causes. K7 inks, or other ink set has more than 3 gray, mainly has benefit of granularity and detail. Neutrality is not a K7 specialty. K6/K7 ink set have no color inks, means you don't have much control on gray shift after chosen ink/paper combination. Other ink, like HP Vivera, may have a much neutral gray inks than K7, and have CMY inks to neutralize gray shift. That's why Piezography made PRO ink, a duo tone K4 ink system.
Regular K3 ink can still get good density curve and tone neutrality under careful control whether using drivers or RIPs. Because my job, I'd tested some RIPs, e.g., ErgoSoft, GMG, EFI Fiery, Onyx RIPs, now mainly use Caldera and barbieri's spectrometer. Caldera has best dark/light (C/LC, M/LM, K/LK) ink transition function. It actually print, measure and calculate an adjustable customize transition curve. For tone neutrality, GMG and EFI has best performance. Both two RIPs support G7 greyscale linearization and repeated calibration function.
We can use RIPs to improve resolution and granularity, that's for sure. Better ripping, dither, and light/dark ink transition can increase quality, but we cannot break the physical limit. Half tone printing is basically using AM/FM method to generate tone value. Lighter tone means less ink dots and coverage, cause coarse grain and low resolution. K3 inks by Epson, Canon and HP limit noticeable range around 0~30%. It's good enough for most user. K7 is a step forward on it.