Almost all people with Black Edition Phenoms up the multiplier.
I've done that with my two x3 720BE's with good results. With a regular Phenom you're stuck using the FSB which makes things a little trickier. Like you said though, it does increase bandwidth, but the thing there is that you have to make sure all of your other components can handle that extra bandwidth, like your RAM. I'm receiving my x6 1055t soon which is not a Black Edition, so I'm going to soon experience the trials of FSB (HTT) overclocking again.
I remember the days before PCI locks and dividers when this stuff was much more finnicky... but I found a kinda special Abit KT266a board that could handle up to 193 fsb, a GF3 ti500 that could handle 83mhz AGP, and an SBLive! 5.1 that could handle high PCI speeds... and I coupled that stuff with some high-speed RAM and a 200 fsb capable Athlon XP chip and ended up with a very high-performance rig.