Car stuff (usually) stays outside. I have so much crap already, she would never know the difference.
The guitars are in the house, so she kind of notices them. I managed to keep one out of sight for two years before I sold it, she never knew I even had it until she saw a picture of it on my computer. She goes, is that your guitar? Nope!
I saw a shirt at Carlisle this summer that said "My wife would kill me if she really knew how much I spent on car parts!" 'Bout sums it up. Probably good that I didn't buy it. :D