Hands down the coolest thing we did on our most recent Vegas trip! Absolutely worth getting a rental car and making a special trip.
The tour itself takes an hour and winds through the junkyard trail of long lost neon Vegas signs. Our docent was full of information about old Vegas, how the signs got to the museum, the history of the hotels they came from, the current status of the hotel, etc.
The price is more than reasonable and goes toward a good cause. You can buy the Neon Museum/Mob Museum combo ticket too if you're into that (we did that but I was less than impressed with the Mob Museum).
A must do! Highly recommended!