Well, if you're an up'n'comer it's of course better to reach a Slam semi by beating, say, the world #1 along the way than by beating a row of unseeded players. People take you more seriously, too: at Wimbledon '99, it was Stevenson who beat Dokic, but Dokic was seen as more of a threat afterwards. But you've got to be good to get to ANY big semi: sure, it *only* proves you can beat the mid-rank players, Emmanuelle Gagliardi for instance hasn't shown herself to be a challenge to the top players. BUT: it shows you can beat them consistently, you can string together four wins in a row, you can pull out the victory with a Tier I QF at stake. Nathalie Dechy put the #1 seed out, but you'd rather be in Gagliardi's shoes right now. She's the one still standing, after all.
And whoever you beat, the winning feeling will *always* be a confidence boost. Anna Smashnova beat no top player (bar Kournikova) in her ten-match streak at the start of the year, but it CLEARLY gave her confidence. (It can sometimes work the other way though - Dokic, Stevenson and Lucic all felt the pressure after Wimbledon, even though Stevenson hadn't beaten any top players and Dokic and Lucic had.)
Anyway, to conclude: brickhousesupporter, you're right: all that Gagliardi will take away from IW is that her game is good enough to take out mid-level players like herself. But she did it consistently, and won four matches in a row in a Tier I - something she'd never done before. It's a step up. And she hasn't been shown that her game would NOT have been enough to take out Kim, had she played her: she has, after all, beaten the woman who beat the woman who took out the #1 seed.