Q1 - do they smell unpleasant?
Q2 - are they dirty?
Q3 - has the functionality (e.g DWR) stopped working?
If the answers are no, you don't need to wash them. If an answer is yes, apply the least possible damaging technique to remedy. Least being a spot clean with a towel and warm water, worst being a full machine wash.
Quite literally the worst thing you can do to shorten the life of your clothes is to wash them regularly. Somehow people got into the mindset that they should wash their clothes all the time, or that their clothes are dirty if they no longer smell of some kind of citrus flavoured washing detergent, which is kind of crazy really. When you're buying materials that are dirt resistant, odour resistant, etc, there's very little need to wash them with any regularity at all, they'll look after themselves.