Will a subwoofer add depth and clarity to my system, or just bass?

A well integrated sub can be transcendent. The key part being "well integrated."
Most hobbyists don't want to buy a sub. They want to buy room correction with a sub attached, and that room correction varies a great deal.

If you can swing it, treat your room first, it will make your speakers sound larger and fuller. It will also help your room like a variety of speakers, including subs.

Audition the sub's room correction. Pay attention to room treatment the dealer may have.

JL Audio has amazingly good room correction, but IMHO it's hard to justify their prices overall.

@jazz99

From my perspective, a well integrated sub can do four things for you

1.  Enlarge the soundstage
2.  Improve the sense of ambiance
3.  Balance a loudspeaker/room that seems too bright
4.  Add a feeling of impact

If you have reasonable flexibility of where you can place the sub, you may not even need room correction or room treatments to get all of these benefits...but with room correction/treatment, you will most likely be able to optimize them.


And with the SVS 1000....if it doesn't do the trick for you...you can send it back.

Subwoofers will not add clarity to a system. They will add impact in the form of notes you can feel as well as sound stage volume.

The problem with them is that very few people know how to integrate them optimally- including the manufacturers!!!. Getting a smooth frequency response with or without room correction is missing the point big time. Subwoofers need to be "timed" to your main speakers- synchronizing the beats at your listening position so that the pulse of the subwoofer is at its peak when the pulse of your main speakers are at their peak.
Getting the timing wrong will cause cancellation and ill formed notes.
Get them timed right (i use the New Order song Blue Monday") and it’s magic.  Just play the music and adjust the subwoofer continuous phase control in small increments until it sounds the best at your listening spot.  
If the sub does not have continuous 0 to 360 deg phase control- forget about it!