I avoid liquid cooling because it is well known that even high quality CLC will lose coolant through tubing over the course of years. At about 5-7 years you will need to crack open the CLC and pour some more DI water in. Thermal paste replacement is a bit less messy, and even then the failure of thermal paste can be more graceful if you make good decision (ie avoid liquid metal).
I consider myself a power user and I'm closing in on six years on my current build. I'm not sure I want to bother with CLC when air has almost as good thermal performance for less money and maintenance.
While I agree with you, if you're building a small ITX system, 120mm AIOs are your only option that can fit in a tight space and offer you good cooling since ultra slim air coolers are too weak for any performance CPU.
In Europe I can find a half decent 120mm AIO for less than $50 ATM.
It's only expensive and messy if you go ball to the walls custom loop.