I bought a D4 around January, and I haven't kept up with any recent changes to the hardware so I don't know what the current D4 models are like (if they have indeed changed). But I will say that the D4 didn't blow me away in its stock form--as shizgeo said, it is a fairly neutral amp/DAC. Especially with a source like the Touch, I wouldn't expect a night and day difference. I do find it very useful as a high-quality, portable and low-fuss (in terms of power) USB DAC with my computer.
With the Topkit from Hiflight, I feel like the amp portion of the D4 improved noticeably. I think the Topkit opamps really synergize with the bassier IEMs that I use, i.e. Westone 3 and Senn IE8. The overall clarity improved, as well as the soundstage and bass quality. There was also less hiss on low volumes with my sensitive IEMs.
My D2000s (which have a warm, bassy sound signature) also have a good synergy with the D4. So maybe it's just brighter, thinner headphones like the K702 (a description based on what I've read) that don't work well with the D4 (at least in stock form)? However, I did notice a substantial improvement with my AD700s after I installed the opamps, and the AD700s are generally considered a bright, bass-light phone.
Please do post back once you get your Topkit, and let us know if there was any improvement.