Hmm. Case 1, if I pay, my expected lifespan extends by 50%. Case 2, if I pay, my expected lifespan extends by 50%. As pointed out by shminux, it's not clear to me that percentages are the right way to go about this. In Case 1, my expected lifespan increases by 10 years (assuming 60 years left), and in Case 2 my expected lifespan increases by 20 years (same assumption).
All of the work is being done by the "money is worthless if you die" assumption. If you ask a question like "how many years of your life would you pay to remove 1 bullet / 2 bullets?" then the answer is obviously different.
Imagine you're playing Russian roulette. Case 1: a six-shooter contains four bullets, and you're asked how much you'll pay to remove one of them. Case 2: a six-shooter contains two bullets, and you're asked how much you'll pay to remove both of them. Steven Landsburg describes an argument by Richard Zeckhauser and Richard Jeffrey saying you should pay the same amount in both cases, provided that you don't have heirs and all your remaining money magically disappears when you die. What do you think?