From my experience with my black car and other dark cars, if you use a blower to dry leftover liquid on a panel after doing a rinseless wash the water will evaporate and whatever is left (polymers, gloss agents, dissolved solids, whatever else) will remain, and it's usually unsightly. So if you're using ONR, Wolfgang Uber, ECH2O, or even McKee's N914, you may notice spots and streaks of residue. I've heard Yvan at Optimum call it "polymer spotting" when they let ONR dry on a surface.
It isn't a big deal at all and the residue is removed easily by re-wetting the surface and then gently towel drying (if the panel isn't dirty). I've left ONR and N914 residue on the driver side glass of my car for a week and it still came off without any concern.
Also, to talk about dissolved solids for a second, have you looked at the TDS of distilled water in a bucket? It should read zero or extremely close. What happens when you put a towel in the bucket of distilled water? The TDS increases. A "spot free finish" can be achieved with distilled water, but if the TDS gets too high it won't matter as much if you started with distilled or tap water. Check the TDS of distilled water mixed with your rinseless wash, put five or six towels in the bucket and then test the TDS again. I haven't done the test in four or five months, but I seem to recall the TDS reaching around a hundred with freshly cleaned towels in the bucket.
The debris that comes off of clean towels is enough to contribute to the need to gently absorb the rinseless residue off of a panel. Different towels will contribute more or less to the TDS of the water. It's worth checking out at least to learn a bit more about what it is that you're dealing with.
