In a way, the remastering seems like a marketing ploy to make more money, to promote the second leg of their national tour (it amazes me that they could still be touring- it's like trying to imagine my parents running around the country from city to city playing rock music every night. I can't.).
Yet, I think it's also an effort to present the music to their fans on CD as it was originally recorded. The pre-existing CD versions are definitely sub-optimal- the transfer from the analog recording is flat and smoothed over. When I heard Rumours remastered, I almost started crying- in fact, I might have. It was clear and vibrant, the vocals had so much more depth, and the instruments stand out from one other- and the singing rises from the music rather than being plastered to it. This is the way it was meant to be listened to. This is the reason Fleetwood Mac is a blues/folk/*rock*- and not pop- band. I can hear vocals and sounds that I never ever heard before- it's just so intense. Definitely worth it