There actually is/was a plugin for the Aural Exciter and Big Bottom with quite a few more controls than the 204, more towards the controls of the 250. But it wasn't a VST or anything, it was for some antiquated "daw" software I can't remember the name of anymore.
At any rate, between the BBE 882 and the Aphex 204... Aphex wins hands down. No contest. Aphex is more of a filler, where BBE is more of a puncher, so I guess pick your poison... but I prefer the Aphex because I can easily add any punch with a simple EQ.
The Spectralive is interesting, but really not suitable for any mastering by a long shot. It's way too over-bearing on 99% of tracks. Not to mention the latest version, 3, has major CPU issues (such as the CPU use doubles when the gui is NOT open).
Personally for mastering in the box I prefer to bring in stuff that's missing, and subtle enough to work great in mastering. You might check out the plugins that Bootsie has been creating lately. He won KVR's developer challenge this year, by more than twice the votes of second place.
http://varietyofsound.wordpress.com/