Ah, you are all correct... State Championship meets vary by the individual states. The more clubs and gymnasts in the state the more "steps" they have taken to streamline the meet to be the best of the best at state, and quite often they don't start championships until Level 4, however nationally in USAG's R&P (Rules & Policies) even Level 4 can be a choice for the individual state board, it just so happens that all the states include L4. Many states still have not adopted the Level 3 program into their state competition structures. It seems the lower population states, such as mine, have to help increase the interest to compete earlier.
I've coached in Washington (and competed there), Ohio and currently Wyoming. Washington has seperated their L4 gyms into "small/big" gym (based on population) and and uses a sectional qualifying system. They also have a fall and a spring state, and some other division of gold, silver, bronze categories, that is new since I've been there. Washington does not have a L3 championship. Ohio also has large gym (national) and small gym (american) division. They further breakdown by age groups, as many age breakdowns as they need to make groups of approx 12- 16 gymnasts competing against each other, i.e. 9yrs A (Jan-Mar Bdays), 9yrs B (Apr-Jun Bdays), etc. There are no sectionals although the first year I coached there, they had North and South State Championships, the last year I was there they didn't. There is a state qualifying score, but all gym's usually set the bar higher for qualification to state, such as 34.00AA. Ohio also does not have a Level 3 Championship. Wyoming is much smaller. Right now we only have one single score to qualify... 30.00AA, but our gym has it set to 32.00 OR consistently place in the top 50% at the sanctioned meets we attended (obviously with a minimum of 30.00). Last year we only had 4 L4's qualify, this year all but 1 (total of 8 qualified). Our 6's are the one's that needed the concession to place top 50%, we just plain old don't have very many in the state Wyoming. As a gym though we feel the right to represent our gym at the state championship should be a earned though. We don't have a State Board sponsored Level 3 State Championship, but our gym sponsors a Championship meet in conjunction with the L4-6 Compulsory Championship. It's brought up at the state meeting every year, they vote no, so our gym keeps having a "championship" with all but maybe one or two gyms that don't bring any 3's. I've heard the reasonings why they don't want to recognize L3 for a state championship, but it is contrary to what the gyms and parents are showing that they want. We feel the state is passing up an opportunity for more revenue for the state. Our gym takes that revenue instead.
In a nutshell, every state is different. Most states have a website that publishes their state handbook and low and behold Missouri doesn't put theirs on the web. Can't tell you what their process is.
Hope that sheds some insight into your search for the importance of state championships and what they truly mean. Probably more info than you wanted to know.