Parables are merely analogies or comparisons--one thing, perhaps unknown or not fully understood, is likened, indirectly, to another that is readily known or understood. Parables are NOT allegories: each item in a parable is NOT meant to be symbolic of some other item in reality or to symbolically represent its action. Parables are really more akin to metaphors than to allegories in regard to their use of imagery. The conclusion or moral that can be drawn from the overall story of the parable, and thus teach a lesson, is the aim of using it.
As for the fig tree parable itself, two hermeneutic considerations need to be taken into account when interpreting it.
First, it is not really symbolic at all! It is a parable and is not reliant on meanings hidden in symbols. The audience knew figs, there were figs on the Mount of Olives where this discourse was being made (as well as olives), and so Jesus spoke about figs. When figs wake up from the winter and put out leaves, it is a sure sign that summer is around the corner. We could say the same thing using trees we know about in our neck of the woods and make the same point Jesus was trying to make, and make it just as well.
Second, Israel has never been symbolized anywhere in scripture as a fig tree, and it wasn't being symbolized as such in this parable. Making a fig tree represent Israel is beyond a stretch anywhere it is attempted, and it is not remotely hinted at, let alone obviously intended, by the language of this parable. To do so is bad interpretation, plain and simple. The fig tree is merely the means to communicate the concept of predictability in sequence from a known event to another related event: if one step of the progression occurs, you know with certainty the next step is about to happen.
Jesus said that when all (Matthew; Koine: panta) these things (Matthew, Mark and Luke; Koine: tauta) were seen (i.e., experienced), then we would know we were at the very end. Those things were all the things, each and every one of them (the force of tauta), detailed in the prior verses. When that condition exists, then the Son of Man bursting through the skies is at the door. The intent is to keep folk from jumping the gun and anticipating the return of Christ before all of these things had come to pass--an especially helpful point considering the length of time envisaged in giving the signs in the first place.
The generation (Koine: genea, all those alive over a particular span) referenced has nothing to do with any symbolic meaning attached to the fig tree, since there isn't any. The point being made was that at least some of those who saw the Abomination of Desolation and its outcome ("all these things") would see the end as well. Clearly, the use of "generation" was not referring to the initial hearers of the Discourse such a long time ago, for the implicit scope of elapsed time within the signs given throughout the Discourse would have made their lifetimes an unlikely frame for fulfillment. So the use of "generation" was a way to push the scale of fulfillment off to a period in the future when the Abomination actually occurred and to offer hope to those believers who would be living through it.
The heavens and earth may seem like bastions of enduring reliability, but Christ's words are so established as to be more certain than even the existence of the creation itself, and especially so in regard to the end of the age.