The premium cabins on AA are chco-a-bloc with people on free upgrades. BA generally do not give free upgrades to anyone, unless they need to move people because a cabin is oversold. Guess which of the two airlines both offers a vastly superior service in the premium cabins and actually makes a profit. I recently travelled in F, with my travelling companion in CW. He is a BA Gold and did not upgraded, nor did it cross his mind that he might be.

I really would advise you not to ask on board, "nicely" or otherwise. It will just cause awkwardness as they have to refuse. However, one of the nicer privileges of First (which isn't true of Club) is that you are allowed a visitor to join you for a brief drink in your "buddy seat" (essentially your footstool) at the discretion of the cabin crew. If you ask after the main meal service, and make it clear that it is just for a brief visit, this ought not to be a problem. See this thread for an extensive discussion of this issue.