+1 to "why not just turn up?"
You have a maximum ceiling to your volume, which is how hard the driver on your amp can work before something breaks. You get there by turning up, and if you turn up all the way it will get there no matter what preamps you do or don't have in your chain. You can boost the signal going into the amp from the onboard preamp of an active bass, or a booster pedal like the Sansamp, or whatever, but at the end of the day volume is volume. What you're getting by adding those things is not final volume but a choice of points at which you can tweak your volume - on the bass, on the pedal, or on the amp itself.
Sometimes people just like being able to do their EQ right on the bass, so they need the active electronics so they can boost and not just cut like on a passive. Sometimes they want the extra gain in the signal before it hits effects pedals. But if all you're concerned about is volume, your amp can't get any louder with an active bass than it can with a passive one.