Very true that, but, the fact that most people don't pay tax at top rate is a good reason for them to vote for someone who says they're going to extend it. If it raises taxes, but it's not coming from their pocket, then people will like the sound of it. If, as seems likely, all parties are, unofficially at least, acknowledging that taxes need to rise, then your average punter in the street would rather see it raised from people better off than them as opposed to on VAT. Plenty of arl arses remember VAT being increased to 17.5% in the early 90's, and it was dropped to 15% in something like 2007 or 2008, before being put back up a few years later, so it's not unheard of.
I'd agree that most people aren't that arsed about Trident, but enough probably are to make a difference here and there