There are 3 downsides to owning an Infiniti:
1. Your monthly gas expense, especially if you're the enthusiastic driver type.
2. Repair bills & maintenance. The cars are very solid, but if you need to do some repair it will cost you quite a bit, still beats any European car in this department IMO, since it doesn't need repair nearly as often. On the maintenance side you need to change brake pads often.
3. It's not really a sports car, it's a great luxury car for everyday use. If you want a sports car, look at something else.