One step forwards... Two steps back.

I seem to be having a bit of a directional wobble this morning.
I re-read the Cornerstones critique of the novel that I’ve been working on to see how I was progressing on the plot fixes, before I launch into the rest of the edit.
Unfortunately, I now realise that I have missed one of the major things that needs to be addressed.  My main character doesn’t have a goal.  The reader doesn’t experience any underlying tension, because they don’t know where the story is heading.
The reason for this is because I wrote the story before I knew the ‘rules’.  Before I fully understood what drives a story forward.  In the past, I avoided writing magazines, and ‘How to…’ books, as I thought that they would influence the way I wrote, and then it would no longer be my work, but someone else’s work with my ideas veneered on top.  The last six months have been a real eye opener, and I have wasted so much time.
The critique, and the editing process so far has taught me a lot, and I now wonder whether I would have written the book differently if I’d known what I know now.
The thing’s that making me wobble is: What do I do now? 
Do I have another hack at the plot, and try to shoe horn in a goal?  At the moment, no clear path on how to do this has presented itself to me.
Do I take the idea of the book, draft out a new stronger plot, and start writing from scratch? This time, making sure that it’s a lot stronger than it would be if I poked around with the existing plot?
Or, should I give this one up as a learning experience, put it on the shelf for a later date and focus my attentions on the new book that I’m writing, that is incorporating all that I’ve learnt so far?
The problem is not that I don’t believe in my ability to produce something that’s publishable, it’s more a case of knowing how much I’ve already poured into the book, and the amount of work ahead to either bring the book up to the next level, or re-writing it from scratch, is very overwhelming.