So I was vanilla for a long time, and still am for most of the time. I really have only tried some out the last week or two on one self contained save. However, I have played mods in other games. Sims 4 isn't the kind of game I would usually consider a mod play candidate (for my personal taste).
So long as a game is sandbox-y and has official cheats, I really don't tend to need or want any because I use it to usually fix tedious things/force games to be a sandbox where there is no sandbox play. Plus 4 (and others like it) updates way too frequently and has nothing Steam workshop level easy to make me really want to fool with it.
When I considered mods for anything larger than that, such as adding mechanics, I realized the scope of things I'd like to change would be annoying to find and maintain. It put me off for a very long time, until I just decided to wing it when I was very bored. I'd only touch things I knew something about and address issues that particularly bother me (such as household limit).
My experience? Mixed. I mean, I did enjoy myself, but my found mod couldn't really surpass the game design for household limits so I have to be careful using it. I noticed a number more dropped actions than usual, too. I plan to delete this test save and remove it all when Cottage Living drops. I may touch it again. May not. *shrug*
So you are not the only one that plays vanilla, but I'd be lying if I said I do not find 4 lacking in some ways that made me bored enough to try them. Beyond stability mods, I wouldn't do that for 3.