JC, like you I had XM years ago and dropped it due to the amount of commercials they allowed for a paid service,,,it was out of control.
I have the 665 and if you just look at the extra cost for the XM radio I agree it doesn't make much sense. For me it was the ability to get the Nav Weather and Nav Traffic through the XM service, yes at an additional cost.
I justified the cost as acceptable given that I know how live real time radar weather on my display and real time traffic alerts. Just last week I am riding along listening to my XM radio, its much better know with fewer commercials, and the voice prompt interupts the music and says, "Rain in the area" I push a few buttons, up pops the live radar, I can see where the storm is and which direction it is moving, determine it is not a problem based on my heading and go about my ride. Later on I am on the tollway cruising along at 70 MPH and the voice prompt interupts my music, "Traffic ahead" I slow down and sure enough there is road construction ahead and traffic has slowed to a crawl. I can exit early and avoid a mess. It also tells me the amount of delay to expect (in minutes) I guess based on changes in average traffic speed.
To me these are awesome conveniences that make my riding more enjoyable and worry free, especially in areas that I am unfamiliar with the traffic or weather patterns.