70/30 is a perfectly fine ratio and works well in tanks. And you're correct, a thicker
juice may not work so well, even though I have used 30/70 mix in my tanks without any problems. Experiment. If the juice is too thick, you can always cut it with a few drops of distilled water or vodka. The coil in your atty will gunk up no matter what you do--the culprit here is not so much VG but the colorings, flavorings and sweeteners that do not get vaporized and end up as a nasty, baked on clump on the atty's coil. The cleaner, clearer the juice you're using, the longer your atty will last between cleanings.
That said, PG itself is not very harsh tasting at all; I often vape unflavored (either pure PG or PG/VG mix) and I find the flavor of PG to be rather mild and inoffensive. Is it possible that it's the flavoring added to the juice, or the nic level, that feels harsh? Nicotine has a very distinct peppery flavor, very pronounced at higher concentrations.