I've never owned an airhead so I'm speaking from no experience, but I'm in the market for a PD myself so this is what I'd do.
I'd upgrade the suspension: Ohlins in the rear and Progressive fork springs.
I'd upgrade the front brake: Harrison 6 pot and associated items.
I'd upgrade the electrics: Omega system or whatever is best.
I'd upgrade the shaft: Rebuildable with zirks.
I'd upgrade the lighting. maybe HID
I'd upgrade to Jesse luggage for the long haul.
Then I'd ride the bike to figure out the minor stuff.
You asked for $0.02 and that's mine.