The other thing about buying a more expensive bike isn't just weight... it's that the higher-end components will shift better, roll a little better, pedal better (stiffer crank/bottom bracket), absorb bumps better (especially suspension forks) and so on.

So it's not just weight. More money is better in other ways too. However I'd never advise anyone to spend more than they feel comfortable with in pursuit or weight, shift performance, or anything else.