Replacing trebles on plugs can cause all sorts of problems if you do not replace them with virtually the same style and weight of hook. The manufacturer of the lure will have finely balanced and tuned the plug to ensure that it "swims" correctly with the original hooks. So it makes a lot of sense to look after and preserve the original hooks as best you can.

My system is very simple, after a trip I hang the used lures on a string "wash line" and spray the hooks with WD40.

There are all sorts of arguments about whether the smell of WD40 attracts or repels fish. Well, I can honestly say that it does not seemed to have affected my catch rate at all. If anything, I tend to believe it has actually enhanced my catch by masking the human smell that we inevitably transfer to any item of fishing tackle, but this could be a long and complicated argument.

Suffice to say I do not think WD40 does any harm, so use it to preserve your hooks and lures.