Yeah, I like the idea of some wonders being purely culture based and others being scientific, rather than all of them sharing one universal system. I wonder if gold wonders and faith wonders could be locked behind religious (a few already are) or economic requirements as well.
The universal system has one major benefit: it is universal. It's easy to understand once you see it. Also, if you start locking wonders behind other walls (like GPT, or SPT, or FPT, etc.), they become 'win more' buttons, not strategic choices. Policies and Science are fairly 'neutral' entities, and play to the two major passive/active bonus systems of the game (policies and technologies). Religion already has a few 'holy city' wonders, and the national wonders, and that's enough to make it separate. Since policies have unique wonders, making the tech wonders an AND system with policies rounds out the pro/con of going heavy science/heavy culture.
In short, the system is as fragmented as it can be without lots of obfuscation.
G