I have both the MixPack and StereoPack plugins. They're pretty interesting plugins, and they can provide some useful sounds and effects. Used subtly, they can be subtle. Used in-your-face, they can sound like dogmeat: but so can any *other* plugin, or external hardware for that matter.
They aren't a panacea for "mastering", but they can sound pretty interesting- and the price is not too shabby compared to the Waves bundle, or whatever other chunk of code you might name.
Get 'em, listen to them, try them out. The freebie download is great for that, even though it knocks holes in the audio every so often. If you like them, buy them and use them. Otherwise, they're just another toy that you probably don't really *need* to make your music. "Life" in a finished track doesn't come from the plugins, to my way of thinking. It comes from the mic and room and player and karma- and, regrettably, the recordist's experience. They ain't figgered out how to bottle that stuff just yet!
I'm going to download their "Vintage Warmer" plugin as soon as I get done upgrading to Cubase 5.1. Not because I think it'll be very useful- but because I can't _wait_ to hear what they think of as "vintage warmth"!