Intruder, I don’t follow your argument, unless you imply that the use of wet speeds always requires full power. Surely an operator could use wet speeds and still flex – runway length, obstacles, etc allowing?
While the wet speeds may not use full power, they will likely use more power than dry speeds. If that bumps the T/O power to TO1 instead of TO2, or TO instead of TO1 (for a 747 using standard derates, as an example), the added use of higher power settings will affect the cost of overhauls (which are controlled somewhat by the %age of total takeoffs using each thrust rating).
The problem with using Wet runway data on a Dry runway is that it's illegal.
The normal rules require that a 35 ft screen height be obtained within the TODA, and that one means of retardation (inevitably reverse thrust) be kept in reserve. That's the rules.
Then, along comes a DISPENSATION for Wet runways (Wet, not Dry or Damp) which allows the use of Reverse Thrust, and allows for a reduced screen height to 15 ft. The dispensation is allowed to be used, ONLY IF THE RUNWAY IS WET!
I doubt it is "illegal" at all.
The wet runway case also assumes a longer stopping distance; also, IIRC, an additional 15% runway length buffer is required for the T/O roll, hence a lower V1 and usually a higher thrust requirement. Only if the screen height or the wet runway stopping distance is limiting, would the V1 or thrust requirement of the dry runway case be more restrictive.
I have not seen an instance, where I have worked out both cases for actual performance, where the dry runway requires more thrust or a lower V1. maybe you can come up with a real-world example...