As far as I know, there's almost no difference in the taste of vg, or at least there shouldn't be if it's pure vg. I have seen a report or two that stated that food grade vg from palm was slightly different but I'm not sure if they done side by side comparisons or not lol. I haven't sampled a lot, but the 4 or 5 different ones I've used all tasted the same to me.
If you're not doing so already, I'd suggest adding 10 to 20 percent distilled water to your high vg mixes. That will freshen it up quite a bit.