The terms of the lease are negotiable at the time you acquire the vehicle. Call around to various dealers and you will find different quotes for the money factor and residual. The dealer's financing arm has a base rate, and the dealer can mark up from there.
At lease end, there's not much you can do with the dealer to negotiate the buyout cost of your existing lease. The financing arm owns the car and is responsible for disposition costs, not the dealer. The dealer's incentive is to get you into another new car.
If you choose to buy another new car from the dealer, there is room to negotiate from your lease. I have been given a trade in credit on my lease to put down on the next car. So, if you turn in a lease with low miles in good condition, its value may be worth more than the buyout clause, giving you some trade in credit. If you the dealer won't credit that value, you could buy the lease out, immediately turn around and sell it, then have some money in your pocket for your next car. A PITA, but could save you some bucks.
Lastly, as others have mentioned, check the tax implications. for Virginia, I pay the sales tax on the new vehicle whether I lease or buy it. But if I buy out the lease, I do not owe any more tax since I already paid it.