Both of the expansions add a lot to the core game play, and I would heartily recommend both when you can afford them. Of the active careers, scientist is fun and the inventions can really change the way that you play the game. Cloning machine. Nuff said. I find the other two careers to be boring and repetitive, but some people really enjoy them. Actives careers do not work as well with large households, so if you play more families, your mileage may vary. The pack also adds aliens, which is enough to sell it for me, but it depends on personal tastes, of course. I haven't really played much with the retail options. The cheapest prefab store is around 70k, so you can't really afford in one in the early game, and I never had much success trying to make my own. I probably will try to explore it more eventually.
Get together is also a great pack. Clubs are awesome, and if used properly they can have positive impacts on nearly every aspect of game play. Properly designed clubs can give substantial boosts to skilling, and can even make your job promotions come quicker through an un-lockable perk. The new social options basically convert the friend of the world aspiration to easy mode. I had my doubts about the pack when it was announced, but I can't imagine playing without it now.
Both of the game packs are worthwhile, and contain almost an EPs worth of content at a bargain price. They are much more focused though, so play style will definitely impact their value. Of the two, Spa day is the pack that most broadly impacts core game play. I basically have a yoga mat in every household now because wellness is so useful for generating moods.
The stuff packs are all skip-able, if money is an issue. I find myself buying more of them than I did in the past games. They are cheaper than they were for TS3. If you can only afford 1, the movie pack is my favorite, the kitchen one is my least.
I'm a sucker for build mode items, so no matter what I'll eventually wind up buying the things.
