Do outboard processors such as compressors, reverb units, etc. have anything distinct advantages in any area today? I'm especially thinking of analog units because of the added D/A-A/D round-trip and all the additional issues this implies. Are there still short-comings of the digital models that can be found for pretty much every piece of famous audio gear by now?
Analog and digital processors work in fundamentally different ways and therefore will always have some differences, however minor they may be in some cases. It seems to be generally agreed that you don't "need" outboard hardware any more per se, however if you want the sound of a particular hardware unit, or if you want an 'analog' sound, there's no better way to get it than to use one of those units.
Now, from a business perspective, if you're running a studio you might want to have some really nice outboard gear to impress your clients, or yourself :)
...Or if you are lucky enough to run tape machine and dBX processing. True some encoding still require you to run on outboard.
And i haven't found a replacement for the H3000s and H3500s.
Then again, when you mean outboard, would you include space echos? Would you include Lexicon L480 and more recent? These units can't be emulated completely as IR doesn't take into account pitch drifts and others. If you are talking of EQ's, compressors, must stuff can be emulated nowadays with low cost to the processor - even spring reverbs and some exotic delays.
As for a room full of gear, I'm lucky enough to record in a room full of gear but I do agree Preamps are a priority and if you are only after to impress (not some nutter that has a heart on AMS RMX processor) you'll be better off putting money on preamps (nice stuff from Avalon to Focusrite red downright to Manley's, Api's and other more exotic stuff you that you might think of) and you will still impress your client with tons of gorgeous gear. That first stage is essential to get it right.
But having said that, if you don't have a nice room, nice instruments, and only a bunch of microphones with a really ridiculous sensitivity and high self-noise ratio, you'll probably better off betting on mixing gear - processors. - Anyone out there with a replacement for a 8051 on a plugin? ;)
Apart from the distinct quality and the distinct "sound" of some hardware devices (which is the most likely reason for using this equipment), there are occasions where digital is not an option, especially when working with DXD/DSD recordings or any other kind of analog recordings.
If you want to record an SACD, the available DSP stuff is very very limited. Or, it could be a choice of taste, i.e. if you would choose to record everything on analog 24 track tape, just because you want the 'tape' sound in your recording, digital plugins are a no-go as well.
The thing with the outboards is the good ones will necessarily give much better sound than any plugins, even accounting for a possible D/A/D roundtrip. And this extra quality will make big difference in tracks where the fx is an important part of their stetic. Compressors and delays come to mind.