My take on DV: Make it require actual diplomacy. This goes beyond a minimalist balance approach, but is there a way to track in-game positive and negative scores based on how many wars you start, bribe others into, or agree to? Maybe -2, -1, and -1, respectively?
I would argue that bribing 4 wars, for example, might cost you 4 World Leader Votes. Whereas brokering peace between other civs might buy you a vote. The bribe/DOW trick is so easy to abuse - but would anyone broker peace and DOW?
Brokering peace, the limited times I've done it, seems like it costs a fair bit. I know I've been able to get Khan to stop warring a CS, but only when his local force got killed off due to my own troop positioning. I am pretty sure I've been able to broker peace between civs - can't recall exactly how expensive it was, certainly more than many war bribes cost.
This mechanic wouldn't eliminate the usefulness of CS allies for a DV, but it would allow for a DV with fewer CSs still alive in the Info Era. (And it would certainly punish a dickwad like Alex from winning a DV, which would make me very happy.) I haven't really thought deeply about this, I just wanted to share the idea.