Yes, absolutely. I don't expect anyone to vape at a nic strength or PG/VG ratio they don't feel comfortable with, but I'm thinking it should be as strong and as close to 50/50 as they're willing, and of course they should include exactly strength and PG/VG ratio they mixed to in their results. In fact, knowing what brand/vendor's PG and VG were used to dilute with is probably information that should be included as well.
I'm thinking of doing it this way:
Initial smell tests. Anyone handy can participate in those, they don't have to be vapers.
Make a single large batch of PG/VG mix. Split it into 5 portions. Add one type of nic to four of them and keep the 5th nic-free. That way each nic can be compared to the other as well as to a nic-free "juice".
As for flavoring, people can certainly add flavoring at some point, but they should start out unflavored!
I think the bottles I have here are 7-1/2 ml, so each sample will be enough to make a decent amount of finished e-liquid.