As a long time fan of the EU i love Mara Jade but i would hate to see them bring her back. Luke saw her when he was doing the whole out of body thing. Can't remember what they called that. Cade Skywalker saw her force ghost in the legacy comics but thats a good way into the future. She could make more appearance as a force ghost but bringing her back wouldnt make sense. And if she was cloned she'd just end up going crazy cause thats what happens to clones of force users.
I would love to see more books about her as a Jedi I believe theres a 5 year gap between the NJO books and the Dark Nest trilogy.
Ever since the first few EU books they ever did, where Obi-Wan basically said "We're not going to show up any more to help you because it's getting harder and harder for us to do so, and you'll be fine anyway" and then never came back, the whole Force Ghost thing has kinda been a bit of a crutch when it is used, because the implication is that for whatever reason, it's just not practical for Ben and Yoda and Anakin and any others to consistently show up anymore. The sheer amount Mara has already shown up as a ghost/force-being/whatever is already straining the plausibility of the whole idea. it could easily be seen as the other authors stretching the rules in a desperate attempt to cover for Mara's death, that wasn't really planned on or welcomed in the plot.
And yeah, Cade also saw Luke, implying that Luke dies at some point. Which of course will never, ever be actually written in in any way if Lucasfilm knows what's good for them, because no one would be cool with it, either in the basic concept or execution. Frankly, Mara could be revived and have the Luke-style implied death in the intervening, what, 150 years? It's a long damn time (besides, I don't really see Legacy as canon. maybe it's just me, but still).
If she's going to be a constant force-ghost fixture, just bring her back and cut out the middleman.
And yes, no clones. But why use clones when you have Plot Spackle, excuse me, the Force?