Keep in mind Free Cities give us another Passive Policy. With Redshore and presumably Blackriver becoming Free Cities (I'd rather not have to pay all that Econ and lose centralization limit) we'd have 4 Passive Policies. At which point grabbing all the immediately shiny policies is entirely doable (defense, city, infrastructure, and vassal/research) and by then- given AN's game philosophy our individual passives will start getting better.
I hesitate to say we should start spamming Free Cities, but in the mid to long term we should keep an eye on ideal regional capitals/Free Cities. For instance, a reclaimed Xohyr to consolidate our grip on the Lowlands, Blackmouth to secure control over our Northern Territory, and possibly something to our East if/when we drive back Trelli expansion.
The idea is as we expand and consolidate our grip on our subordinates we to some extent replace them with productive and dependent Free Cities to further project our reach.