Servers will always benefit from faster CPUs and more RAM.
Improvements in CPU and RAM for servers translates to either more clients served, or a smaller server in general because the growth of the technology has exceeded the growth rate of the transactions being processed.
For desktops though, the resource usage has indeed slowed down considerably, due in no small part to the 32/64 bit changeover holding back a lot of software.
Considering that my 3.4GHz Pentium 4 HT from 2005 is still able to reliably perform all of the basic computing tasks- internet, email, media playing, and storing personal data, I believe technology has reached a plateau where simply increasing the performance is no longer enough to bring about another radial change in how people use this type of equipment.
Now its just a game of making it cheaper and more energy efficient, while the market is saturating because there is far less of an incentive to upgrade all the time than there used to be.