Non standard bottom row, so can't find replacement keycaps.

6.50 spacebar is virtually impossible to find except at MaxKeyboard (39USD for full set replacement keys).

Otherwise quality is ok, build also ok.

Google k70 led failure.

Changing keycaps is great. The usual keycaps are of lower quality (thin, not so good material), while aftermarket keycaps are shine-resistant, solid and sounds better when bottoming out.

Important thing is that the switches last a loooong time, and the keycaps will start to wear out long before, so...

It's up to you really.

Also, most LED keyboards will fail over time because the LEDs don't last as long as the switches.

Every keyboard that have LED, the LED will tends to fail at some point because the life of LED is much shorter.
Even you get Ducky, Deck, those LED will fail too. You can change the LED. Not big deal.

By default, the stock keycaps coming with corsair keyboard is ABS materials. For long time use, the keycaps will become shiny, not like when you buy new.
Some people do not like to type on these shiny keycaps, then they will change a new 1. Maybe other materials like PBT or other kind.
Some change because some keycaps really beautiful.