So, personally, I own every single EP, but I don't own every single GP. Vampires is the only GP that I could argue feels like an expansion pack, because it comes with a whole new gameplay set with a new world and LOTS of build mode items, but other than that, I just can't see GPs outperforming expansion packs.
I don't own every GP, and it's just because it's too narrow of a focus for me to want them. I have parenthood and vampires, but I can't see myself enjoying dine out or spa day or anything else like that. I feel like with expansion packs, even if you don't like certain aspects, there's just so much stuff included in them that you'll find something you enjoy.
Like with Get Together, I've hardly ever used a club during my entire gameplay but I use the European architecture build objects as well as play in Windenburg religiously. It's my favourite world. Same with City Living; I might not go to the festivals often but it seems like every day I'm discovering a new clothing or furniture item from the pack that I never saw before, and then I fall in love.
I think for people who can safely afford the price tag of EPs (they are pretty pricey), they're worth it.