KTC, you have to find what works for you. Personally, I prefer to tackle one major writing project at a time. But I don't consider poetry or flash fiction "major" works, in that, a handful here and there are not all that time consuming. Now, if you're consistently writing 3-5k short stories, that could get distracting.
I don't see the point in distancing yourself from what you've done. You're freaking out man. Agents don't care if your past publication history is "unfocused," and I highly doubt they'd come to that conclusion about you anyway.
In August, I got my first work of fiction published (flash fiction) in what I'd consider to be a pretty legit literary magazine (about a 5% acceptance rate, maybe a tad less for fiction.) I'm proud of this. Is it selling a novel? No. Was I paid? No. But I still got my work out there. People read it. 5-6 actually took the time to comment. I think that's an accomplishment. And even if I manage to finish my wip novel and sell it for six figures, I will still be proud of that first accomplishment.
I think you're dealing with two separate but interrelated issues here.
1. You want to focus on one aspect of your writing.
2. You think distancing yourself from what you've done before will help you toward that end.
But I don't think that's the case at all. Everything you've done and written up to this point determines what words come out of you now. So if you want to focus, then focus. But there's nothing wrong with taking a break. Doing something you find fun, even if it is a different sort of writing.
I'm going to venture a guess here. If I'm off base or you want me to delete, just let me know... But if I remember correctly, you have that play production on the 24th or 25th, right? And you mentioned it was time consuming... And because it's been time consuming, you probably haven't had as much time to revise your mss and get it to the waiting agent. So now you're worried about how you might be coming off as un-serious and you're trying to apply this to all the writing you've done up to this point.
But, here's the thing. Normal people (unlike moi) find writing fun, and you seem to be one of those kind of writers. So you should do what makes you happy. If you want to concentrate on novels, do it, but that doesn't mean you can't work on other stuff here and there, and that certainly doesn't mean pretending your existing body of work doesn't exist.
People have read your stuff, and enjoyed it. People have seen your plays, and enjoyed them. How do you think they'd feel if they knew the person who wrote them wanted to cut all that off because he was afraid it made him look un-serious?
I know I rambled a lot, but I hope you get what I'm saying.