Hi there,
Sorry no one answered sooner!
From what I've heard, Love Hina Again contains substantially more fanservice/ecchi material than the original series. I also heard that the plot wasn't as good, either, bordering on nonexistent. Personally, the Love Hina Christmas special is one of my favorite anime episodes of all time, and is about the same as the TV series content-wise, if not a little better. ^_^ I haven't seen the Spring special, so I can't comment. Hope that helps, though!