In reply to jhw:
If your footwork is rubbish, new shoes will make no difference.
If you have excellent footwork, then they will make all the difference.
On slabby routes, aren't you smearing more, and not really using small edges?
What sorts of grades are you climbing?
I've always used big, sloppy shoes, and only now, after 20 years, do I feel that different shoes really matter (and that is only when doing somethign pretty technical, like bouldering). If your shoes are huge (like mine) then your foot can roll inside the shoe itself - so your foot comes off the shoe, which then comes off the rock.
I would keep your £90 (from what you have said and from looking at your profile). Experience will improve your footwork - just concetrate on placing your feet very precisely and carefully, rolling your foot onto the holds.