Well, here's the short version...

All was going well in gaming a girl, as I was in the stage of building rapport. As rapport was being made, I did a cold reading, and then we started talking about Astrology...

While I didn't know anything about it, it's one of her favorite hobbies. So I thought "What the heck" and told her to tell me whatever she knew about my sign.

She told me much more than I thought she would, and here's the big problem:
EVERYTHING was right. Spot on. Not a single flaw.

Being shocked, I researched the other signs, and they weren't nearly as accurate.

So I've started talking with friends and other girls about it, and it's accurate on them as well. But more importantly...

It creates great rapport and an interesting topic. It's a powerful gaming tool especially during comfort. Now the problem is... How much should I flaunt around with this? I fear that, if she knows that I'm getting obsessed with one of her hobbies like this, it'll seem try-hard and false.

So what do you think? I want to close a LTR with her, so... Should I keep this level of fascination a secret from her? Should I wait until some time has passed? Should I wait until I've kiss-closed her?

You dont have a problem here! Its a good thing that you've learned something new and now you and the girl have some common topics to actual talk about. Share with her on your learnings and she might find it cute that you actually made the effort. Let her do most of the talking.

As you start having women in your life you'll have lot many more situations like these - women love to learn about a lot of different things and they love to show that intellect side of theirs. You can learn tons from a lot of good women, dont miss out on that opportunity.

Just can't shake the feeling it will drop me into the LJBF-zone. But heck, comfort is all about common topics that intrigues both parts, so you're probably right.

Having sex with hot women in all it's fame, but actually appreciating a woman for who she is rarely happens me.

Wrong mindset. Don't artifically act like you like a hobby more/less depending which one we/you think is the more fruitful in getting laid. Let conversation flow naturally and don't feign unnatural interest/disinterest in stuff - that icecream will probably lick back.