Exactly! You get it. My process is simplified to: concept prototyping with simple shape graphics -> mechanics debug & stabilize + graphics "facelift" -> debug/adjustments with 10+ other players' feedbacks. I'll check out Illumin-Mates tomorrow :)
That's more or less what we did, it's a solid system. Except we only had a couple playtesters... that's fantastic you could wrangle up that many! Awesome! Hope you enjoy it!