My opinion,
In theory compressors are basically the same thing. All they do is put a threshold on the sound with an attack, release, and a ratio, sometimes others, to control the dynamics.
But in reality, compressors react to the audio differently. So what you need to remember is that your buying a compressor based on what its doing to that sound.
Maybe the problem with digital compression is that its just done too simply. Its doing exactly what its supposed to do and doing it too perfectly. But what you need to decide is whether thats a problem or not. To me thats not always a problem. If i really am just trying to control the dynamics and im not looking for anything special, than ill use a basic nuendo plugin to do it.
With analog, and some of the nicer digital plugins that simulate analog, its probably the imperfections with the circuitry that makes the compressor react a special, colorful way with the audio.
So with that all in mind, i dont think the cheaper analog stuff is going to be much more different than a decent digital plugin. The RNC is generally described as pretty accurate and smooth. With using less transisters and other chips there is less interference with the sound. So i dont really feel that an RNC will give you a much different feel of a compressor than a decent digital plugin, except that its outboard and you can use it in a few different ways. And if you are using Nuendo 2, you can compress on input to control clipping anyway with a plugin.
Xstatic brought this concept up to me once when we were chatting and it really got me thinking. The Alesis 3630 is considered a pretty crappy compressor around here and else where in the audio world. But the thing is, it does exactly what its supposed to do. You just shouldnt expect anything more than that. If your not pushing it too hard and your not clipping it on input or output than it does a decent job at compressing. I personally never felt the coloration was never to horrid on those things if your using it right. But the problem is, it doesnt add anything to the signal. Its just really plain. And if you use too hard or wrong youll hear the major artifacts of the crappy components that its made out of.
Im not saying go out and by a Alesis 3630 because i think you can get better for the money. But theres a concept behind it that helps you understand what is really going on in the large world of compressors.
And the RNC really might have a smoother sound and cool coloration compared to the decent compressor plugins. But is it really worth going out and spending $300 to get that when you dont really know what that coloration really is? When your ready to start learning the differences maybe but to expect it to completely change the sound of your recordings its minimal in my opinion.
Danny