So after more playing around, it turns out that one of the plugs had gone bad. I'm thinking it was because of the dodgy lead, because after I replaced the lead, then replaced all the plugs, the issue hasn't come back. So it's running how it should now, which is nice!
Re: windscreen, bit the bullet and am getting O'briens to put one in for me on Friday. $808 later (though they are including free chip repairs on it for life, which is worth about $150 I think she told me), I'm gonna be a bit sore in the wallet but then at least it's done (And I only JUST passed pink slip the other day, he told me I passed but that I have to go get it replaced, and I'd rather this guy not get into trouble as this workshop has looked after me before on numerous occasions).
Matt