Having Owens and Romo would be sweet at times, but I think keeping Plax for the long haul is better. I realize you want to win week 9 in particular but I don't know that I'd trade away your guy who's red hot. Especially since Romo appears to be fading a bit after his incredible start (sorry, I know he's your QB but I'm underlining that because as you said, if you have the tandem setup, one sucking kills both players) and the Giants appear to be gaining momentum.
I think you're WR core are strong. I wouldn't tinker with it and instead hope that Stallworth gets in on the action week 9 when his team faces Indy. Indy has a tough pass d going, but I think Moss and now Wes will get all the attention, leaving Stallworth to make a show of it. I am predicting that to be Donte's breakout game actually.
Keep in mind that week 9 Romo/Owens faces a strong Philly pass attack too.
Thank God for Football Season.