If it has a powerful magnetic field, 3/4th G should be more than enough to hold onto an atmosphere. A magnetic field has a lot more to do with keeping an atmosphere than raw gravity, because it keeps it from being stripped away by solar wind. Look at mars, for an example - Its magnetic field died long ago, and the sun slowly eroded the atmosphere away, but its gravity is only a third of earths. Titan, on the other hand, has only 1/6th earth gravity, but has a healthy atmosphere because it's protected by Saturns magnetic field. Also, argon, being heavier, would make for a denser atmosphere, so you could achieve earth-like pressures even with the lower gravity (if you want to.)
As for the composition itself, neon and argon are just as inert as our nitrogen, so whatever life there is is probably going to be oxygen-breathing. Oxygen is the most reactive element in the universe, so it only makes sense to use it in your biochemistry. That being said, if they were to visit earth they'd probably suffer oxygen toxicity, since they're used to breathing a very rarefied mixture.
As for the lights, sure, why not? It might actually be easier for them to develop the technology - Gas discharge lamps simply excite Argon/Neon/Xenon/Ect until it starts to glow. We have to contain the gas in a bulb because if we don't it'll diffuse into our nitrogen (and non-Argon/Neon) atmosphere. On the world you're talking about, something as simple as a static spark would have an orange or violet glow. I'd imagine them having some very pretty thunderstorms.
Side benefit: Any kind of Taser or Laser weapon that has a mundane invisible beam on earth would be very vibrant and colorful on their world.