Oh man, Sausage Fattener and Soundgoodizer....where do I begin on this subject?!
In my honest opinion I think they are completely over rated, and a quick fix to make something "Sound" bigger. But in reality I believe they can mask underlying issues within a mix, causing problems later on. I used to always want to use something like these back when I was 1st starting out, because I wanted that immediate Awesomeness to my tracks! But over time I've found I can get a bigger cleaner sound by use of careful EQ and level monitoring, and then get the fullness I desire with parallel compression and some subtle multiband dynamics at the end of the mixdown process.
Each to their own I guess, but in all honesty, I wouldn't use Sausage Fattener if it was given to me for free.