Perhaps these ideas already exist. If so, I am sure you will let me know in the comments. If not, and you are a game designer, and you steal one of these ideas, please send me a copy of your game so I can play it, which it will be impossible for me not to do, because these ideas will make playing your game so goddamn easy it will be impossible to resist.
Idea #1: Your book has a book jacket and the book jacket is a DM screen that has all your during-play charts on it--hits, saves, major weapons & damage, whatever.
Idea #2: You see those cupcakes in the picture? Those cupcakes look tasty because they came out just right and they came out just right because the cookbook they came out of was comb-bound which means when it was time for Aunt Suzie to pour the frosting on them, the book was lying flat open on the chopping black and it was easy for her to add the eggs before the cream hardened because she wasn't fucking wasting her fucking time finding fucking paperweights to hold the goddamn book open.
Comb binding is more durable than spiral binding, less soul-abrading than that 3-ring binder thing they did in the 2e monster manual (I see why you tried it guys, but...no), and probably cheaper than traditional binding. And if you just made a book that's full of magic spells I'm gonna want to look up, there's no goddamn reason on God's green earth you shouldn't use it. Especially you, retro-clone guys, because I know you want to save a buck and because you know whoever's buying that player's manual is probably buying your game for convenience more than for how majestic it looks sitting on the shelf next to Bartlett's Familiar Quotations.
Wanna stay classy? Laminate it.
Idea #3: Speaking of spells...Spell cards are a nice idea, but you know how they tend to disappear and then show up months later stuck to the bottom of a leopard print platform heels with chihuahua bites out of them and Rocco Siffredi's cell number scrawled across the bottom in sharpie? Ok, maybe you don't, but I'm sure you get my point: why not make a deck-of-cards sized spellbook--1 spell per page--bound with comb-binding or some other hole-punched flippy binding? Better to have one spell book people can hand around and point and go "See? A save is allowed only if and only if more than one tentacle enters the orifice..." Which, yeah, reminds me: leave blank pages for homemade spells.