I do not like Occult Lexicon; it's not a bad card in any way, just the first four words in the text complicate matters significantly: "limit one per deck":
Given how long scenarios typically last, and the punitive aspect of weaknesses that punish over-drawing, Arkham Horror LCG tends to leave a sizeable stack of cards left in your deck by the time a scenario ends, where even cards you've included two copies of have a chance of not showing up for any one scenario. This makes single copies in your deck very unreliable, and depending on them showing up early is ill-advised.
And Occult Lexicon value depreciates significantly the further into the game you draw it. After playing only one copy of Blood-Rite, you've broken even in terms of tempo: one action to play Occult Lexicon and one action to play one copy of Blood-Rite nets you two cards, two resources, two damage, or any combination thereof in two actions, what you would've gotten with basic actions. To get a return on investment, you need to draw one specific card, play it, play the other card that just entered your hand, wait till you draw one of the two remaining copies of that card, and then play a third card; a feat made unlikely to occur often with the deck limit.
You could always tutor Occult Lexicon out, there's Backpack and Research Librarian for that, but I advise against it, as it compounds the slow nature of Occult Lexicon. Now instead of spending two actions to get something back, you're spending three. Tutors are much better spent on impactful cards that you would be willing to spend two actions to have now rather than one later (or one and zero respectively it the card is fast). Occult Lexicon enriches your deck with better than average cards with high flexibilty; it's immediate impact is lacking.
Now despite all that, there's one sterling example of when Occult Lexicon might very well be an auto-include; in a Marie Lambeau deck. Marie wants spell assets or non-fast spell events to make use of her special ability, and Occult Lexicon enriches her deck with not just above-average cards, but above average spell events, eliminating their slow nature somewhat as they might as well be fast cards when played with her additional action. In addition, Hallowed Mirror works exactly the same as Occult Lexicon in this regard (and Marie can take both, as the're both lvl0 occult cards), with their respective spells being all-purpose enough that you're happy with drawing either. With that in mind, you can treat Occult Lexicon and Hallowed Mirror as a pair of a single card, just like any other card that you can include two copies of, which eliminates the other downside of those cards.