Evil twin/clones are a huge, huge sci-fi cliche. You have that cheesed-out, cliche reaction to deal with right off the bat. It can still work, but it has to be damn good.
There are a lot of original aspects to Data and the Soong androids, a sort of mini-mythology going on. Lots of history which told us a lot about Data. Thomas Riker worked because he had more dimension, and also because of the subtext of the story, similar to that of "Tapestry".
But Sela just doesn't work as well. The cliche overwhelms the situation. She might have been a far more interesting character if NOT played by Denise Crosby. Nothing against her, but when she emerged from the shadows as Sela, my reaction was of the "give me a !@$#%^* break!" variety.