the kids had fun, you didn't have to stress, your 9YO was involved, sounds like a win-win in my book :-)
IMO, a wise parent knows that the whole birthday-party-arms-race craziness is generated more by parental worries/expectations/succumbing to advertising than by a real understanding of what kids would enjoy. Most of my now-10YO DD's b-day parties have involved snacks, simple art projects, and running around on the lawn (my most brilliant discovery when they were in kindergarten and first grade - hire a couple responsible high schoolers to help out. They're energetic, not afraid to act silly, much more budget-friendly than the professional clowns or magicians, and the party guests follow them around like they're rock stars!). No theme napkins and plates (honestly, have you ever heard a kid say "the party was fun but the paper plates sucked"), fairly minimal decorations (signs my kids made), but the kids all had fun and neither my kids nor their friends complained that it was boring because it wasn't at a place with trampolines or mini golf LOL.
And the easiest party so far was their 10th, when they invited a half-dozen of their friends over, ate spaghetti and meatballs, made lanyards and friendship bracelets, and watched a couple movies on our little 20" TV before eating brownie sundaes.