I agree with pretty much everything you are saying. The only thing I've really noticed is that some flavours fade over time, case in point being the gingerbread I'm vaping now, it was mixed on the 28th June, so not that old and the ginger has faded to half what it was.
Now if you prefer the flavour with the ginger much more subtle then you could say this mix gets better after a 3 month steep, but that's totally subjective.
I guess if you've used concentrates that you don't like the taste of, then it might taste better after a couple of months too for the same reason.
Personally when I get a new flavour first thing I do is mix up 10ml and if it tastes like shit I don't use it.
That last bit of advice is what I learnt in the hard way i think - I went trigger happy and whipped up 300 ml of different recipes that came to mind and in the process wasted some expensive nicotine I'll be doing much smaller mixes in the future and nicotine - free first!
Thank you all for the input!