It depends.
If you only play TS4: yes, it's most likely enough. Currently, all of TS4 takes up about 35 GB on my system (although for the most part, I play a vanilla game, so there's not a lot of CC/mods clogging up space here - but 35 = base + all currently available DLC installed).
If you only play sims-games: it'll probably still be enough. Especially if you decide to install only one on your SSD and the rest on the HDD (I don't even think TS2/3 benefit all that much from being on an SSD, but I might be wrong). I only have 4 on my SSD currently & 3 + 4 on the HDD. I somehow doubt I'd notice much of a difference if I had put 4 on the HDD instead (loading aside), but I'd have to test it first to really have a reliable opinion on that.
If you play a lot of games: it could still be enough, honestly, especially if you only put one or two games on the SSD - that is, games that actually benefit from running on one (like to reduce hitching in open-world games). But, still, at this point, given that you're playing a lot of games & that SSDs are generally more energy-efficient, smoother and quieter, I'd probably consider going with a slightly larger one anyway. Although I'd still keep some games on the HDD.
All that being said: keep in mind that SSDs are mostly only good for reduced load times (including in-game loading), but don't otherwise impact in-game performance all that much. For TS4, especially, the most important thing for performance is your CPU.
Hope that helps!