Has KDE adopted the windows-strategy, where you need to buy new hardware everytime you get a new version?
I don't think so, some people says that kde3.2 is faster than kde3.1, I am not quite sure, I believe they are as fast. But I haven't run any benchmark.
You may try to delete (or move) your ~/.kde directory and try to see if kde is running faster. In fact it's a good idea to have a fresh config directory after an upgrade.