They were spammable before. With the newly added adjacency restriction, how many you can get in a single settlement gets greatly restricted. Nerfs their late exploration gold generation, but - more crucially - because all of the Caravanserai buffs are through civics, not traditions, you don't carry any of the buffs through. All you get in modern is fewer caravanserais, and a pitiful 3 gold per trade route tradition.
On the whole it feels like playing them in this new version gives you more production but less gold in exploration, and straight up less gold in modern.