Two ways to look at it:
1. Cost savings
2. A profitable outlet for shade tree moders
#1 For some the cost numbers are the main point and for most mods this is a good yardstick to use. For some mods it is more for item #2 (say a swap to a manual trany if the current one is not broken). In this case the point of the mod is doing the mod instead of moding for more HP or performance.
Both ways are fine by me
