At least with my Topre Realforce 87U there are definitely some perks to justify it:
* The feel of the mechanical keys is fantastic. There's much more feedback; keystrokes make a nice subdued "schlock" noise. The backspace key sounds like the sound from Mario games where he does that spinning landing thing on a baddie.
* Easily swappable keys; my WASD are swapped for the purple arrow keys they come with, and my Esc key is a nice dangerous-looking red.
* LEDs are built into the keys they're for. Not a killer feature, but pretty slick.
* Flexibility; there are dip switches in the back for various tweaks such as swapping Ctrl and Caps Lock on a hardware level - they even provide keys to switch out so that the new Caps Lock key gets its LED.
For something I'll be typing on for many hours a day it's a worthy investment.
Those all sound like neat aesthetic benefits, but the OP made it sound like there's something objectively wrong or buggy with less-expensive keyboards.
It's largely subjective; the feedback of mechanical vs. membrane keyboards can certainly be measured objectively (i.e. pressure for key presses and snapback time), but it's just a matter of personal preference between the two (and I wouldn't consider the better feedback to be just a neat aesthetic benefit; it's the reason I bought it, not a bonus). My dad has always used an old clacky mechanical IBM keyboard but has no problem using membrane keyboards. I can use a membrane keyboard if I have to, but now it feels "mushy" after being spoiled by my Topre.
Membrane keyboards are cheaper to make (because most people don't care) but have less tactile feedback and are less reliable. Mechanical keyboards are more expensive to make, but are much more durable (keys will not wear out) and have quicker key snapback. Lack of n-key rollover could also be considered a defect of inexpensive keyboards, although it's not a common hindrance to casual typers.
* The feel of the mechanical keys is fantastic. There's much more feedback; keystrokes make a nice subdued "schlock" noise. The backspace key sounds like the sound from Mario games where he does that spinning landing thing on a baddie.
* Easily swappable keys; my WASD are swapped for the purple arrow keys they come with, and my Esc key is a nice dangerous-looking red.
* LEDs are built into the keys they're for. Not a killer feature, but pretty slick.
* Flexibility; there are dip switches in the back for various tweaks such as swapping Ctrl and Caps Lock on a hardware level - they even provide keys to switch out so that the new Caps Lock key gets its LED.
For something I'll be typing on for many hours a day it's a worthy investment.