No. The only time when it's sensible is if you take less than 2~3 months to recoup. After that, difficulty would likely increase to the point where you will lose money mining unless electricity is free, or BTC shoots up in value.

I arrived at that conclusion while calculating if I should just put together a few 6 GPU sets. This was further reinforced by others who arrived at similar conclusions when taking into account increasing difficulty.

On top of difficulty increases, I also took into account USD devaluation, it's been on the slide for many months relative to my local currency so makes it even less attractive to invest in a full rig.

Adding one or two GPU to an existing system however may be worthwhile.