re: "...I know those wonderful CFL's we have been sold for homes do not keep their brightness, so wonder about LED's...."

I don't know if your car has LEDs, but to discuss them, let's start by saying that they and CFLs can't be more different. Compact Fluorescent Lamps are fundamentally the same fluorescent lamps that have lit rooms for half a century or more, and like any fluorescents they have hot filaments (to emit electrons that energize phosphorescent coatings on the glass that in turn emit photons of light) -- such filaments, as well as the "starter" circuitry, wear out from heat, etc.

LEDs are based on an entirely different effect, a solid-state phenomenon in which certain combinations of crystaline elements emit photons when current passes through them.

Bottom line, there's absolutely no basis to compare their lifespans. Typically, LEDs are often rated for 10,000 hours, although every technology has some flukes where a sample will deviate from the norm.

Some baseline info: I have a 04 V70 with 140,000 miles. I checked today and had no problem with reading the instruments in sunlight with sun glasses on.
I am not sure if the dash lights are on during the day(?, but I turned the setting to minimun with no decrease in being able to easily read the instruments.
My wife's 2003 V70XC is the same.
Art