The main worry you've got is usually something like Paris filling the Louvre with great works and then the Communards taking over. Everyone who goes on holiday to the City of Light comes back humming the Internationale. But there's other things to keep an eye on if you want to avoid losing the battle of ideas with your own people:
- Religion. If Rome founds Catholicism, converts you, AND gets the World Congress to declare Catholicism as the world religion, the Pope's condemnations of greed are causing their ideological pressure on you to almost double. (Even if none of your people are Catholic, the influence of the World Religion on politics will give the Holy City a bonus to influencing you.)
- Trade routes and open borders. Those Chinese trade ships and tourists are dropping off little red books that increase ideological pressure.
- Diplomats. That Russian agent who's in your capital and letting them do extra diplo is also having academics over for tea and increasing their ideological pressure.
- Music tours. That English great musician wasn't singing Love Me Do; it was The Red Flag, giving Comrade Elizabeth a big pile of free ideological pressure.
If you're struggling to keep a sprawling empire happy, then a compact empire packed with luxuries with Dictatorship of the Proletariat is going to get a bonus as your minimum wage workers envy their delicious free lunches.
On a related note, if Brazil gets Futurism, expect autocracy to get really popular as their Carnivals spit out experimental works of art that carry Pedro's fascist message.
So yeah, ideology is about cultural popularity as accounted for by Tourism. It's a good idea to check the cultural landscape every era, and if someone's got a load of great works making them influential, taking them out before they found an ideology and draw half the world and your own disgruntled masses into their sphere of influence. Or just produce so much happiness that your revolutionary wave is too busy partying at Woodstock to organise an effective protest.