All very sound and logical thinking. However, your whole argument is predicated on the assumption that the markets will continue to look negatively upon the Tories' plan. I am not at all sure that this is the case. There was an initial shock and immediate drop in the value of the pound, but that quickly recovered. You might argue that is because of expectation of higher interest rates and that may well be a part of it. But on the other hand sudden drops (or rises) in the value of currencies (or stocks for that matter) are pretty much always followed by a swift movement in the opposite direction shortly afterwards. Markets usually overreact - you see it all the time. Something will be at say 10.00 one day, some news comes in and it drops to 9.00 immediately, and then next day it's back up to 9.8 (or whatever).
I don't think you can say with any certainty that the pound won't be moving upwards over the next few weeks. The BoE said it would act further if necessary. It may not be necessary.
Seems to me people on here are VERY much too quick to throw the towel in. People were calling the plan a failure after less than 1 working day, which IMO is a ridiculous attitude. Sure, you can disagree with it in any timescale you like, but you cannot call it a failure until its demonstrated to be a failure, and at best it will take several months - a year or more potentially - until we can see whether this is working or not. New investment into the UK and new confidence in the UK isn't something that you can magic up. You might argue it's never going to happen and you may well be right. But we don't know yet.
EDIT: You have also to consider that at some point speculators will start to think the pound is so low that buying Sterling is a good bet, and it will start to rise. Bear markets don't last forever and we've been in a Sterling bear market for the past 18 months. Ditto, many analysts are saying the dollar is over-valued and it's been on a bull run for too long.