I'm sure it matters to some buyers, but not all. I'm also fairly confident there has been an uptapped market up until this point, of people who have wanted a high performance prestige luxury midsize sedan, but also with high reliability. The Lexus GS F is poised to be the first to deliver on this. We shall see in the near future how many buyers the GS F gets, despite not having the "marketing special" 500hp mark.
Maybe you are right, I hope Lexus can hit a home run with this car. However, I don't think Lexus ever intended the GSF to be a high volume vehicle (and I don't think it'll be priced to be), I think the intention is to be a halo 4 door sedan for the brand. That I think we can all agree on.
My confusion with the GSF is, if its suppose to be a halo vehicle, why position the GSF below the main competitors in some of the most valued purchase reasons for a vehicle in this segment?
Also I'm not sure what you mean by "high reliability". I agree that the German engines have higher maintenance cost but I'm not sure if they are less reliable if proper maintenance is done. And I'm not sure someone spending 80-100K for a performance sedan is overly concerned with cost of ownership, to a point of course.