Got the splitter on my coupe and my coupe dropped on its ass as well. Speed bumps not an issue clear them no probs all i hear catching now and then is the exhaust. All I recommend is watch out for rolling front end into kerbs if your astra is lowered as it will hit the kerb. As i found out when i left my car to get mot'd and the tester rollled the car into the kerb when parking it up in the car park and chipped the splitter and broke 2 of the bumper mounts (Got a cheque for £250 as couldn't be repaired GSI BUMPER MONEY 😃).
You can see it doesn't look like i got much ground clearance , but I've never worried about speed bumps and I got them awful full length of the road style speed bumps as well in my village. Hope this helped bud. Plus when i see a standard front end of a coupe, I always think the spiltter makes a hell of a diference