To put things in perspective a little bit....
I bought two new mopeds, Peugeots, back in 1978 and 1979 from a local bike shop here in Sacramento, Ca. I think the prices were $299 and $399 a year later for an upgraded bike with signals, etc.
Okay, new mopeds out the door in "1980" dollars. 28 years later, what is the equivalent in today's dollars? Depending on what assumptions you make for inflation, you will be approaching an equivalent in today's dollars of about $2000, or more.
Add the fact, there are few moped manufacturers today, and vintage mopeds in good shape can be hard to find, it appears that most mopeds are really undervalued.
So, if you can find a moped, that has been refurbished by qualified technicians from scratch, and would be considered, "good as new", what would be its value? Tough question...
In the end, according to economic theory, prices are determined by willing buyers.
Also, that is one reason I haven't sold many mopeds, as I can't find buyers that value them as much as I do, and I am not willing to give them away.
End of my two cents worth!