Any tricks to tightening the dash above the speedometer that rattles over every bump?

Was your dash recently reassembled or has it just developed this issue over time?

Did you try pressing down all around the top of the dash in that area to try to more firmly seat any of the zillion "push on" connectors which hold it together?

There are instructions around for disassembling the dash, look in the thread about fixing the capacitor problem. My guess is that if you took it apart you would find missing or broken connectors. Connectors which you may or may not be able to replace. Alternatively, find a bumpy road with no traffic and press down in one spot at a time to locate the loose spot or spots. Those will probably be where the broken/missing connectors are.

While you might not be able to replace the broken connectors which allow this rattle, you might be able to reduce or eliminate it by jamming a bit of shock absorbent material into the right locations to damp the motion. The rubber from a shoe insole could work. The dash would still move a bit, but as long as it isn't making noise, you can probably live with it.