RE: Monster Variety
I think it's important that the monsters
have an ecosystem.
So you don't wind up with "what the heck is this ooze doing hanging out with this orc?!", but you also don't wind up with "all of these kobolds are starting to look the same to me."
I think easing up on combat in general will also help this -- if there's only 6 combat encounters for each level, it's easier to avoid repeats. And note that "combat encounters" effectively just mean minis-grid combats. You can, say, fight a sea monster while on a ship, or a colossus attacking the town, in a much different way than you can fight a group of orcs. Think of
Shadow of the Colossus or
God of War or even some of the immense critters in
Final Fantasy XIII. There is a lot going on there that isn't just "I hit, and do damage, and inflict a condition."
I'd also say that I would like
fewer monsters per encounter. Make use of elites and solos, not just as "boss monsters," but as regular features. Those 6 combats should be
dramatic.
If a combat ever feels like filler, it's probably best to jettison it. Battles for life and death shouldn't be boring. Make at least 3 combat encounters per level an actual struggle for the PC's to avoid TPK, and make at least 3 noncombat encounters per level something that the success of the current strategy ultimately relies on. Risk death and failure. Don't play nice. Even,
use fewer encounters, but make those encounters MORE EPIC. You don't have that many pages. Pick three solos at Level +3 and let the PC's figure out how to take them down.
And that way, when you do have these encounters with kobolds, you have fewer of them, making the fact that there's only 5 or so varieties less of a pain.
Part of what I think would help is an actual system for noncombat encounters that makes use of character roles, archetypes, and powers, in the way that combat does. But noncombat roles and powers are things I've been advocating for a long time, so I might have a bit of an axe to grind on that point.
But that way, whether you're killing kobolds, or negotiating with the king, everyone can contribute, everyone
risks something, and everyone stands to gain with a success, in a unique way that is resonant to their archetype, rather than in some generically broad way.