That 3M Lime Green is a very nice color choice and illuminates quite well.
I'm actually doing three sets of channel letters as we speak. I'm using a custom coated Yellow Green RE Phoshpor CCFL behind it instead of white. I did some light measuring and I got nearly twice the light output instead of using white.
Depending on who you use for LED's you probably save about 35% in energy consumption over neon on magnetic transformers, neon on SST breaks about even. Judging from the size of your CL's, you chose right using LED's.
I am curious though, on who your sign guy used for his choice of LED's. Looks like some of the modules may already be going out. It's always up to the fabricator to use what's proven and lasts a longtime.
Again, nice sign!