I couldn't play LoW without it! Adds a bit more game while keeping it easily accessible to newcomers.
They've said they plan on another expansion sometime. I hope it beefs it up suitably to become more of a gamers game.
I'd rather it didn't. You can overburden a game very easily trying to do that. Lords of Waterdeep is a good entry-level worker placement game, but if you want to go deeper you're better off playing something like Viticulture or Archon: Glory and Machination instead.
I played Viticulture with the Specialist Workers from Tuscany for the first time last night, and honestly I don't see myself wanting to play without them again. We drew the Professore, who lets you remove a standard worker that you played in the same season and use it again later, and the Traveller, who can take an action from a previous season. The Traveller didn't affect much as he is more useful on the Extended Board where you have four seasons of actions instead of two, but the Professore made for some really interesting play. Players often put out their standard workers early to take bonus spaces and so were picking them up again with their Professore, which freed the bonus space to be used again by someone else. This was how I eventually won the game; in the last Winter season the player before me picked up his worker on the Winter Visitors bonus space, which allowed me to play two instead of one. I played the Advanced Judge to trade a wine for 3 VP and the Manager to take an action from a previous season without placing a worker. The Judge let me tie the leader for points, and I used the Manager to take a tour that gave me enough money to win on the first tiebreaker.
There are eleven Specialist Workers and you only play with two of them, so there are still nine I haven't seen. They do all kinds of things ranging from letting you claim the bonus even if the space is occupied to forcing other players to pay you £1 to play on the same area of the board. If you like Viticulture, you should absolutely buy Tuscany - it's a whole new game.