It's a know fact that everything that goes in or out of the cat5 cable in the 360 is being logged by the "big dogs" in the modding scene.
The banning that happen have always(so far) been because something is wrong with the backup that the people were playing.
Don't get me wrong there is a risk playing on xbox live with a console that has had a firmware flash.
You alone will have to decide if modding you 360 is right for you.
As for me.
I have 2 small girls.I have handed them a 360 game to play.They turn around drop the disc then step on it all in 1 sec.
The disc is trash.
That is the reason I have modded my console.
The disc that my girls have ruined have more than payed for a new console if this one gets banned.
Like i said this is a decision you your self will have to make.
I for one think (at this time ) it's worth doing.