I guess you want some cash now, but this is one of those names where I think it's in its infancy. With gas prices, cost of vehicles, and pollution concerns, I think the next half-decade will see a real increase in smaller, cheaper, less-polluting forms of transport like this.
Although it's a well-known word and item, you don't see them everywhere yet. I can't remember the last time I saw one (I'm in Canada). And the term doesn't get a lot of searches compared to other wheeled vehicles.
I think with a well-developed site, with some much broader appeal and info than you have on there now, and with nifty SEO that reaches even into fuel-savings, pollution-reduction, etc., you could significantly increase the traffic here... and sit on it for a few more years.
Vehicle manufacturers are updating/re-releasing items all the time that are based on old trends and new world circumstances, and I can realistically see the moped making some kind of bigger appearance.
It's entirely an educated guess, of course, but it's not a long stretch.
Right now, undeveloped, I'd say the use/popularity/value is in the grey area for this name. It's a real item, but not in use/common everywhere.
Still, somewhat common word, known item, useable/sellable product still being manufactured: I'd say realistically, and not taking into account whatever traffic stats you have:
resellers = 15 - 25K
end users = 40 - 60K as a good minimum. If you can really, really interest an end user who manufactures/sells them, and especially if they are planning new products/larger market, then easily into the low - mid xxx,xxx range.
I think this is accurate and hope it helps you some.