Imshi goes into this better in the "which jet" post. The Harrier has a high accident rate and is slow. If we ever do operate jets again in the future, it will be in small numbers. Less than 20. So the idea of getting something like the Harrier would be a mistake, in my opinion. If previous Air Corps losses are anything to go by they'd never be replaced.
The Air Corp need something economical, reliable and effective. The Harrier is effective but thats not enough.
The question of dispersion in the event of war is a bit of a non issue for me. I went into this before in another post. If we were ever to be invaded we could never operate any jet in the numbers required to be an effective force. Either we'd be invaded by the US or the UK (not gonna happen) or by some nation who had already beaten the US/UK - so ever 400 Fast Jets would really make any odds.
The F-5 seems the most likely option - however I am seriously put off by its age. Grippens or the like are the way to go, alas I cant see that kind of money being allocated.