Resistors

Resistors do not wear out. Some people will swap them out for what they think are better transistors but I am sure Wilson uses good parts. Some capacitors can deteriorate. As far as I know the ones use in passive crossovers do not. 

If you are not happy with the sound work on room acoustics. That is where the money usually is.

Never - You don't need to change resistors or transistors.

How often do you burn them out? 😁

Not sure those above that said don’t change have ever owned Wilson’s but maybe have. The resistors you are referring to are not in the crossover, but resistors used as a fuse to protect the tweeter and drivers. They do weaken in time if they’re played hard. The ones dealers and Wilsons recommends are the tweeter and midrange driver; the bass resistors likely do not need replaced. There’s a panel to access these as the components in the crossover are potted so you’re not getting to those. I have not replaced the resistors on my WP6’s and they sound great. My dealer is looking at the cost for the tweeter and midrange which I might change out. Go through a dealer as they may help you out on the cost if you have a history with them.

visually, you can see a transistor that has bone bad, you will know when you see one.

otherwise they last forever, most of mine from the 1960's are good, a handful replaced, cheap, easy solder job..

typical +/- 5% of their stated value in the old days, now +/- 2%,

can you hear the difference?