I don't think $25 is to steep for what they are offering but I do feel that $20 is the sweet spot in terms of a good price point.
They had this up at the official forums but then it got taken down for some reason
New content includes:
4 New Vehicle types: Motorbike, Monster Truck, Dragster, Drift
15+ Additional Licensed Vehicles
60 New Tuning Kits
Unlimited FreeDrive Multiplayer challenges
Like I said earlier, the FH2 Storm Island Expansion offered only 5 new vehicles for a $20 price tag, Wild Run is offering 15 new vehicles, 3 times the vehicles for $5 more. Not to mention the new dynamic weather system, and graphical overhaul that everyone gets for free, updated locations on the map, new gameplay modes in the form of Drag, Drift, Bikes and monster trucks, new physics, the new summit area and events and so on. I don't think $25 is obscenely high considering what you are getting, but would I like $20 instead? Yeah, sure I would. I suppose I could wait for it to go on sale next year, but I probably won't wait 9 months to play something to save $5, not worth it imo.
I think if you don't already have the game then The Crew complete edition is a very good deal, Base game plus Wild Run, plus the season pass for $59, that's a lot of bang for your buck.