How many people at these events? More than 5000? I had about 6000 at the MLK March a few weeks ago with no issues using an Airport Express II on 5 Ghz. (DL16S) I was up to 125 feet from the router. It does sound like you're doing everything right to me. 5Ghz does have less range than 2.4Ghz, but I'm sure you know that already. A better router will never hurt you, but it also might not help you and I hate spending money without a reason. (Though routers are pretty cheap.)