Probably the most important thing I can say about meditation and intelligence is that you can go too far on it. As Britton said about side effects, you can decondition important signals (including traffic signals), and that there has to be a balance. Some stress is actually healthy, but we have to pick and choose more carefully. You want to let go of ruminating about things that distract, and cognitive therapy helps to zone in on inflexible thoughts that aren't realistic. That means to relax the body and thoughts and return to your activities. There are a couple of things I learned so far about high performance learning that you need to condition MORE of to develop intelligence:
1. Anders Ericsson pointed out that engaging with a skill really well (even if slow at first) is necessary. After you've staked out what a high quality procedure or skill is, then do enormous practice. This way you are not practicing mediocre skills. There are lots of studies of Deliberate Practice, especially with Spelling Bee's you an look up.
2. In conditioning psychology class there was a practice I learned, that sounds a lot like Thinking Introversion, where you create clear definitions of what you want to learn. One of the ways to do this is to create true and false testing questions. You define a concept you want to learn and use as many
examples of the concept and
non-examples to test yourself. In the textbook they said that doctors use this. This way you are able to recognize when something is or isn't when you encounter phenomenon. A lot of mistakes in work involve not recognizing what you are seeing, and therefore not being prepared for it. The more thorough your IS's and IS NOT's in your practice, the more thorough you understand a topic. You can use a diamond example. "What I'm seeing is this side of the diamond and it's also not the other side." When you know a subject really well you'll know because whatever is thrown at you, you know what to do, and if you've been practicing #1, then you'll do it really well.

So #1 involves a lot of effort because of the practice and #2 involves a lot of cognitive processing to understand a subject. All these drain a certain amount of energy, but if you have less worrying thoughts that interrupt it, or low self-esteem issues about what you are capable of, these practices will be engaged with more and you'll learn faster because you're not
spending time worrying about psychological baggage. If you have psychological baggage, you can still do the above practices and get good results, like most non-meditators, but it's less efficient.