I have no idea where the OP is from. However, First Class on most US domestic flights means a bigger seat, possibly a meal of some sort, and possibly IFE (depending on the airline/equipment type). You don't fly it for the "luxury" that you might find on longer international flights.
The exception might be flying on, say, Virgin America (with its very limited route structure). I would never pay alot of extra miles or money for US domestic First Class.