This is a bunch of crap. Check out this paintjob i did WITHOUT stripping anything. It depends from bass to bass.
But everyone knows that if you leave the old finish on there it will adversely effect your tone...
But yeah, I personally wouldn't bother about any stripping unless you are planning to re-finish it with a semi-trans finish or a burst.
Most cheap basses have a poly finish, which makes for a great primer. Its also night impossible to strip without a lot of elbow grease.
My first re-finish involved these steps:
1. Take off the neck and everything else (pickguard/electronics/bridge)
2. Rough up the surface with about 300 grit paper to make sure everything sticks, then wipe it all down to get any dust ect off.
3. Spray over the whole body with an undecoat, same brand as desired top coat if possible, do this a few times (3 or 4)
4. Spray desired colour, every two coats sand with finer and finer paper, smallest I normally use is 4000 grit, though plenty of people will use microfibre stuff and go down to 12000 +
5. Clear coat gloss if you want. Helps protect the finish too.
Ive probably forgotten something, so have a read of all the guides ect on the net.