Well, it's true that the extras are mostly worthless. The area is kinda slow and uninteresting, and it takes a long time to get good items out of it.
The Lost Sanctum has some good rewards, but it's essentially a series of fetch quests, a few of which are driven by random drops/appearances (a very, very bad thing, IMO). I don't mind its concept, but climbing up Mount Emerald over and over is a pain, and while some of the new bosses were interesting and even a bit challenging, overall it's nothing too special.
The dungeons in the Dimensional Vortex are pretty cool, with good design, some new dialogue, the use of the Mystic Mountain soundtrack, hidden treasure, solid overall. The permanent stat gains are great rewards on their own, especially since Lucca needs speed badly. Some of the new items are great, but they're just items; these things shouldn't be important enough to care about. Also, it's all too short to be considered a "deep" or truly worthwhile set of bonuses.
The ending is a mix. It's frustrating, a lot of people hate it, and since it successfully ties the plot to Chrono Cross (a rather polarizing love/hate game), it only enforces that love/hate divide. I'm okay with it, I guess, but I sort of prefer pretending that Chrono Cross doesn't exist. I'll blame the whole multiple dimensions thing and sit in my room knowing that in some dimension there's a conclusion to CT that goes exactly how I want it to.
So yeah, Greg. If you're playing it for the new content alone, it probably isn't worth $40. I'm getting it because it's one of my all-time favorites and I haven't played it in ages - this is a good opportunity to replay it, max out a file, then put it away for another age or two.