One of the things not mentioned so far about Ducs is they don't like to go slow. Slow, as in legal speeds. Even my '03 SS750 didn't like to cruise at anything under 90 mph. That doesn't always make for nice encounters with the boys with flashing lights. Adding that most Ducs come in 'look at me' colors doesn't help either.
If you want one and have the cash to spend, go for it. They are fun, unique bikes that handle very well. You can spend more money than Paris Hilton pimping one out if you want to, (Pie boy probably knows all about this), but you don't have to do that. If you want to do the wrenching yourself the maintenance costs aren't really a factor. OTOH, if you take it to the dealer as often as they want you to, you can have a second mortgage payment, just signed over to the Duc dealer.
Dollar per mile, it's not really worth it, IMHO. You'll never ride the Duc very far, or for very long at any one time. Its fun, it's a cool bike and very visceral, as well as visually appealing, but do you want to ride or have rolling art to talk about when you're stopped?
Do what makes your pants feel tight.
which might mean having another slice of pie.