I really like all the comments.
I've definitely considered the 500 series things because you can swap them out etc. It's a nice way to build at lower incremental cost.
My concerns with the 500 series are power supply and the trouble of routing stuff around.
Right now, I have EQs in my RME. I can run a mic into the RME, EQ it, send it out to my DBX 162 SL, then back into the RME. So, in this case I have access to EQ before or after the compressor. It's a lot like what you'd get with the Neve Shelford channel. I can even blend the tracks together after the EQ. It doesn't give me the Silk setting, but there are plenty of saturation tools in Sonar.
I kinda have 2 routes for Shelford like hardware EQ and Compression mixtures with my RME and DBX mixed up.
But, ok, and here's the point where you say 'OMG He's Lazy!'.
I don't want to have to get down on my knees and futz with the cables all the time. I can have the Shelford Channel plugged into the RME all the time. I just plug in the mic and go.
To really play with the sounds of my DBX and my RME, I have to click things in the computer then dial things in on the DBX then twist things on the computer again. It's really not a problem per se. I then get 2 or 3 tracks recorded into the DAW... 1 is the original mic track, 1 is the return from the DBX, and the third is the loopbacked mix of the DBX and the original mic track.
Now, I'm in mixing heaven.
So, if I want more than 2x this setup, why not get another 2 channel compressor and now I've got 4x the setup.
I don't really have a good answer. There's no good reason for me to want a Shelford Channel or a Portico II.
I think over time I've realized I don't really need every possibility in the box. I can just print something that sounds good straight away and use it. There's only but so much time I'm going to spend polishing things. Having a tool that makes it easy to get a pretty sound seems like a nice time-saver.
I remember the liquid channel pre-s on a Focusrite I bought once (didn't keep it b/c it was buggy with my laptop's firewire and while it worked at first, as soon as I flashed the firmware it never worked again). That thing sounded so deliciously creamy. I still remember how it made my heart leap when I first used it. Then, I was crushed when it stopped working.
My RME and Audient Pres are nice and clean, but I'm not sure that clean is what I like. Whatever that focusrite did, I'd like to have some of that. :-)
So... there you go. I'm saving my pennies.