Well you are at a LabVIEW based community forum so I'm going to guess most people would tell you to stick with LabVIEW because of all the diverse fields that LabVIEW is used on, and for the large range of hardware and applications.
That being said careers can change, and it may be a good idea to try something new. Keeping your options open is always a good idea and by trying out PLC and learning that field puts you in a better position down the road for other employment opportunities where you can say you are both familiar with PLCs and LabVIEW, but are not an expert in LabVIEW.
It's your decision to make, but don't worry about if you made the wrong decision down the line. Things can always change and you can choose the other path in a few years if things don't work out. Or take on a completely different career that has nothing to do with programming.