Yeah, I'd agree. I think they could easily make them about 50% more expensive to build, and maybe make them doubly as strong. Even like Dur-Sharrukin, I think it would be better if it was +5 fortification strength in this settlement and +1 science on fortifications in all settlements. Byrsa could probably give you +2 gold on each wall in that settlement, or maybe even make it global as well giving +1 gold on walls in all settlements. Even abilities like that are not really game-changing, but sort of like the change to the Great Stele, would just make them a bit more balanced on the whole.
I don't want them too expensive, though. I think in the past civ games have often fallen into the trap of making them so wondrous, that especially on higher difficulty levels, early on, when you're fighting for land and territory, it just is too much of a cost to even think about building them. I like the fact that I can be expanding out my empire, but maybe it is worth my while to circle around and grab the Stele or Gate of All Nations. I'm not giving up too much of my empire to try to build them.
The other part of wonders that needs a little rebalance is to make sure the civ wonder unlocks are a bit more balanced. Like it's weird when it takes longer to get to Hale o Keawe in the Hawaiian tree than it does in the regular civics tree.
