Great topic MBurras! A little more involved than people might think but lighting is always in interesting topic. And as always, I have a few "cents" to offer. I only entered the hobby 6 months ago but lighting is one of the first areas that garnered my attention since I sell commercial LED fixtures for all lighting applications; both exterior and interior. I set forth to determine color temperature that best accommodates my preference. Both Steven and Randy have been very helpful with sourcing and I've purchased lights from both Randy and dgwojo. Randy was very helpful and after much discussion, sent me all four sets (including bi-pins); original incandescent, Warm White LED's, Cool White LEDs, and Blue LEDs so I could evaluate my preference.
Warm White LEDs
I anticipated the original color temp of the incandescent lamps to be somewhere between 2800K and 3000K, which should have been the same color temp of the warm white LEDs - and it was; I recently pulled the original meter lamps out of my 2265 and replaced them with the warm white LEDs and was pleasantly surprised to find the color equal to the original lamps so, if my goal is to restore to original factory cosmetics, warm white is the choice.
Cool White LEDs
I replaced the same meter lights with the "cool white" LEDs (est. 4500-5000K color temp). This color temp is typically what most consumers are familiar (the LED look) with and expecting when they replace shop lights and various other lights around the house). This color temp provides much more blue output than standard incandescent lamps and is the most common for retail and commercial lighting. When I replaced the meter lamps with these, the meters really "popped" with a greater saturation of blue from the entire meter panel. I really liked the results of these just as Steven indicated. Yes, it takes one farther from the original look but it's not an astronomical leap. Again, simply a matter of preference but as many of you have stated - not really an upgrade as far as the performance of the unit.
Blue LEDs
I'm not really going to spend much time on this and I'm not sure of the color temp but for the sake of brevity, IMO the blue was simply far too much and made the unit look like a toy. The nomenclature on the meters also became less noticeable.
Upgrade or Preference
I think it's really a matter of perspective as to what one decides to call these modifications. If our perspective is "lighting performance" then yes, I would say using the term "upgrade" is appropriate as you are installing components that both run cooler and last longer. Unfortunately most people considering this term will tend to apply it to the overall performance of the unit, in this regard, using the term "upgrade" can be a little deceiving. And while they certainly consume far less energy, you are typically adapting them to run off of the same supply voltage as the incandescent lamps; therefore, there is no benefit gained by their increased efficiency. I guess if you actually modified the unit so that the 8v supply could be reduced to 2-3v (reducing the stress on the power supply) it would improve our position with respect to the term "upgrade," however, the gain in efficiency by reducing 5v of supply voltage, would likely not result in any tangible audible performance enhancement.
Again, great topic and always interesting. Sorry for the length of this post but I enjoy discussing lighting and hearing everyone's opinion. And it certainly is a matter of opinion. I really consider myself more of a purist and will likely stay with the "warm white" colors. I just "relamped" a Yamaha CR1000 and sourced some "cool white" LEDs from dgwojo with green condoms. Once again, everyone reflects on the Yammies as having the "greenish" color to them but when I installed the green condoms, it was far too much green IMO, just as the blue LEDs for Marantz units. I noticed that the Yammie had something already built into their meter housing that caused the original incandescent lamps to provide a yellowish/greenish tint. I removed the condoms and the unit looked 100x better and original IMO.