[quote name='ITDEFX']The Sela character had SO much potential and would have been worth bringing her back several times during TNG's run.
Heck they could have brought her in for DS9, but didn't

[/QUOTE]
I'm glad.
I disagree about Sela. It was a bad idea, however well-intentioned. Because the crew had no idea what happened in Yesterday's Enterprise, the whole thing comes off as rather WTF. The main characters don't know how to react, and resolving the whole Romulan-ness/Tasha-ness of the character proved too difficult. She was just a Romulan that looked like Tasha and had some awkward conversations now and then.
Sela was also wasted because what do you do with her? Her very existence begs the question they can't answer: why don't you go back and rescue Tasha or, well,
something. Yeah, yeah -- can't mess with the timeline and all that.
But it's already been messed with, and that's a crew member that was stranded in the past. Or, rather, an alternate timeline crew member that was stranded in the past. It's a can of worms, but it doesn't make it better by ignoring it. Oh well, alternate timelines...what do you do? La, la, la! Look, a Romulan!
Some ideas sound better on the drawing board than in practice.