Does it help if a pet is highly intelligent or not? I'm too lazy, atm, to read books to the pet I want to use for battle. Plus I'm only interested in being a casual battler. Like for the time when there's special items, the current stone ones, or when there's a plot the needs some battling.

You need a certain number of alchemy points (one awarded per 16 intelligence your pet has, awarded on the 16th only if you read a book to your pet) to use scrolls. But otherwise, no you don't really need it, at least not as a casual battler.