I've seen some users setting volume higher than the GUI allows, & claiming that the output's poor.
I also recall reading that Nokia kept volume low-ish, because there's too much reverberation.
The same could be true for vibration. But, the only way to know is to experiment (carefully) I guess!

Lets see what they say in the "bug", they may give pointers on how to adjust vibrate via the terminal (prolly already doco'd for the N900).
We have to remember what CG explained about the bug-tracker though, they're not Nokia Support.