I have a WR camera body (K-7) and all my lenses are non-WR, although I often work outdoor. Let me share my own experience.
With the zoom lens, one issue is the risk of water/humidity getting into the lens during the "pumping" action of zooming/un-zooming. This can be reduced by carefully wiping regularly the lense with a dry cloth, but it is a worry.
The other major risk is swapping lenses. In bad weather, I simply refuse to swap lenses unless in secure, dry conditions.
On the other hand, I have much less issue with my prime lens (Voigltander Nokton 58mm). The lens is very sturdy and is almost WR.
Ultmately, however, the most important is to take care of the lenses and of the camera. Remember that WR is not weatherproof nor water proof. WR = weather resistant only. Your camera and your lenses need TLC (Tender, Love and Care)...