Yes, 9 is worth it, especially if you have a crossgrade deal available. I am in post production, so I tend to stay up with the versions as they come - 9 is a huge step up. You wouldn't notice if you aren't using it for large mixes, time code, etc. If you are just a home user or using it for post on your recordings, it is not a necessity to upgrade; but, eventually 8 will become unsupported and the deals to cross over more affordably are usually offered for only so long. (This constant upgrade cycle is my only complaint with Avid - it is the only way for them to continue to drive revenue). Best advice, if you are happy and have all the power and tools you need, stand pat. If you want to get deeper into it, see yourself more as a "power user" or generating revenue as an audio professional, keep up with the larger upgrades.
Multi band compressor is not standard, that will have to be a purchased plug in. Waves L3 has been a standard and very good. Wave Arts (different co.) makes one that is very good and probably the most affordable
http://wavearts.com/products/plugins/multidynamics/ I am a big fan of McDSP products -
http://www.mcdsp.com/index.php?option=com_content&view=article&id=41&Itemid=271 Any of these purchased plug ins will require an iLok key and account set up to make use of the licenses.
Also, the Avid audio forums are a great resource. There are many active professional mixers and users participating there:
http://duc.avid.com/