Depending on the surface that you race on, the "replacement" schedule can vary. Back when I owned an XRay, I found that the quality of the parts allowed me to run the car for an extended time without having to replace anything. During the indoor season I would tear the car down once a month to check for damaged bearings (rear outside wheel-bearings would go bad with a good contact with a wall) and worn parts - however, I rarely had to replace anything. During the teardown, I would check and re-oil bearings - look for suspension slop, or cracked parts and change shock oil.
Unless I was in a really bad crash on the track, I would just go over the car in between qualifying or practice rounds to make sure no screws were loose, etc. Keep in mind that we race indoor carpet here in Canada (www.fastcats.ca
) - with XRay being the most-used car, I rarely hear anyone complaining of having to replace parts too quickly. XRay diffs are one of the best in the business so you can go a really long time without having to rebuild them as long as you build them as per the manual.
I think rebuilding has to do with how you drive the car vs. the chassis itself. Now that I am running a Losi, I go through the same steps and also find that parts don't wear much as long as you keep everything clean. If something needs replacing, I replace it right away before it gets really bad and causes other parts to fail.
During the outdoor season, I tear-down the car after the race-day to make sure I get the small pebbles and dust off the car - again replacing what is broken or worn.