Worth it assuming that they require the extra power and other bells/whistles over that of a MacBook. Also assuming that the rumour is in any way true. There is constant speculation about new products from Apple and whilst a few turn out to be accurate to some degree there is no way to know what Apple will produce until the actually announce it. Whilst there has yet to be an Intel based replacement for the 12" Powerbook it seems somewhat late for Apple to introduce one now. The PowerBooks were the first of the range to go Intel, back in Jan of last year. The entire range was Intel based by August of last year.
I'm going to assume that this average of £300 you mention is based upon buying in the US with a student discount compared to regular (non education) UK pricing. Otherwise I fail to see how you come up with such a large 'average' discount, given that a quick glance of UK regular pricing compared to UK education (not HE) pricing reveals discount of £0 for the iPod Shuffle up to ~£137 on a base spec Mac Pro.