My wife says I have too many guitars and motorcycles. Is it conceivable that there could be too many guitars or too many motorcycles?

Concepts like “enough” or “too many” are inevitably dependent on context. Too many for what purpose?  Obviously, the key question is going to be the Standard Model; do your guitars and motorcycles require us to abandon everything we thought was true about physics?  If not, they probably won’t be a significant problem.  You might helpfully point out to her, though, that if she’s even thinking about this, you may well have enough motorcycles that charming young ladies desiring of your intimate attentions cannot climb over them all, get bored, and go away; she will doubtless see the appeal.

And why does playing a guitar while riding your motorcycle down a mountain give you pickles?

Because it loves you, and it remembers that you have eight different t-shirts bearing the cryptic legend “I like pickles, give me some.”