Actually more optimization is taking place than visual refreshes. Porting the stuff to Qt5 (esp. QtQuick2) should speed everything up on non-ancient PCs.
Visual refreshes are just easier to explain. ;-)
Its not speed I'm bothered about. KDE is more or less very smooth at that. Its the resources it takes! The CPU is always nearly being utilized on a small-medium scale, and nearly 700mb is taken away at boot-time and gathers upto 2gb upon usage. That's too high, at least I think so.
Would KDE actually require so much for all the features it gives or can that actually come down?
It affects the performance of the system! By "smooth", I referred to KDE's UX, which is more or less smooth. But the overall system performance reduces due to less resource when you run some heavyweight tasks.
The CPU thing is either a bug or file indexing is not yet complete (although that should not take more than a few hours).
How much RAM is utilized depends on the components you loaded. "Convenience distros" tend to start more services by default. The KDE Workspace is very modular. You can disable/remove many things, esp. if you compile yourself.
That said, it's not a workspace primarily for low-end computers. If it requires more RAM than your PC has, maybe look at LXQt.
KDE devs are known to live on the bleeding edge. A lot of people complained about it when KDE moved from v1 to v2, v2 to v3 and v3 to v4. But KDE remains targeted to 'relatively recent' desktops.
It might not be that big of a problem this time around, when(ever) we move from v4 to v5, because hardware isn't evolving as fast as it used to. But KDE will remain a behemoth.
Well, on kubuntu you can install kubuntu-low-fat-settings (not sure if they still offer this):
sudo apt-get install kubuntu-low-fat-settings
Basically, it turns off composting and file tagging services. It reduced the memory requirements and the CPU % dropped to something close to GNOME 2.x or XFCE.
Are you sure you are counting that memory usage correctly? Because altought KDE consistently uses 6GB on my machine by some metrics, the total used memory at the same time stays under 1GB.
Would KDE actually require so much for all the features it gives or can that actually come down?