What cost per extra 1mph on bike?

[Slaav]

So, having been seen off by an admittedly much fitter chap on a sexy blingy bike at the weekend, I was wondering if i upgraded my bike to a blingy one, would that (and ignoring fitness improvements etc) give me an extra 1, 2 or 17 mph average speed?

So, get off my Allez triple on to (eg) a mid range carbon with 105 or Ultegra, would that extra (eg) £1500 give an extra 0.3, 0.9, 1.5 etc mph?

What do you reckon? Obviously, I am not simply trying to buy extra speed but just want to make my extra speed more 'attainable' and get up to approaching 20mph average if at all possible.....

Any ideas or pointers? (Aside from the obvious MTFU!)