I'd say its worth it, no reason not to do it, really. I lost my Diablo 2 discs a while back so i bought a cd key off a 3rd party website for $1.50 and was able to download the full client off Battle.net after registering it.
do you happen to remember that site? my LoD disk got fragged and I havent been able to find a place locally that sells just the expansion?