First off, I think you will be fine with Stafford as your QB going forward. With the weather changing outside DET will be playing their next 4 of 5 games either in a dome or in warm climate (ARI). Plus Stafford has scored 3 TD's rushing so his potential to be more consistant long-term for you is there over the other QB's you listed (though Palmer has a chance to put up nice numbers while he is on a hot streak himself).
Second, don't drop Mendenhall just yet. He will eventually gain the starting job back and when healthy he is a load to take down. The Steelers will need their running game till Ben returns so hold on to Mendy as RB insurance down the road.
Third, I wouldn't drop Miller either because Batch will need him on critical passing 3rd-down plays. Batch is no stranger to the Steelers offense so he should do fine till Ben returns. I like Meyers a great deal but would drop someone else instead if you want to play Meyers over Miller in the coming weeks.
And last, if you do drop someone it should be A.Brown first over any other options. Alexander is available and can help your roster now. Hillman would be a great pickup as well. And it would be hard to drop DJax as well but if you can guarantee a chance to pick up any hot WR prospect to help your team now then I can see that scenario playing out. Would be hard to trade DJax now that Vick is down and the PHI organization is a mess offensively. The only reason I would do it is if you have a legit chance to reach your league playoffs with dropping DJax and acquiring a player you can insert into your lineup the remaining weeks. Otherwise I would wait and see if Vick returns in the next week or two.