I am the author of Real Eurekas, the mod that adds new eurekas/inspirations and randomizes them when the game is started. Always interested in a discussion about them

My position on the topic - great idea, badly implemented. It's fresh for a couple of games, after that it's just another min/max mechanism which can be and is exploited. My guess is that Firaxis implemented it for people who don't have hundreds of hours in the game and will never have. And suppose it's ok from their perspective, because those people make up a majority of buyers.
Saying that eurekas increase replayability is the same as saying that tech tree increases replayability. It is there, it is known, connections and paths are already defined, etc. What's more to add?
Eurekas by definition should be unexpected. They actually cannot be something one can plan for. Ofc this approach is not entirely possible to have in a game, which is a simple computer program, so some kind of compromise is required. The mod allows to hide future eurekas, so they are revealed along with the progress of the game. Plus each tech has a few possible eurekas that are chosen at random.
What remains to be done is actually define those eurekas. Define in a way that is meaningful and achieveable through normal gameplay. This is the biggest challenge and difficulty. It is easy to take one or two techs and invent 3-4 eurekas. But there are 117 so hundreds of them are needed, each one exclusive and tailored for a specific tech.