I think it depends on your situation. If you just play at home, jam with friends, or play smaller venues - they're pretty much worthless. And it's not an "effect" that you gives you flavors. But once you start playing bigger venues, they become almost essential. Imagine a guitarist with snarling distortion a no noise gate, that's what happens to your bass signal. Well, sort of.
I currently use the Aphex Punch Factory. As light (settings-wise) as I use it anyway, it works great. I'd definitely recommend an optical compressor over the limiter/enhancer type units...
I used to have Art Tube pack. Some might say it is a mic preamp, I can agree, but do try it with bass!!!! It works, you can adjust gain (overdrive the signal if you like). There is also a small led display that allows you to adjust the compression or limiter. The little wonder costs about 150$ and I am seriously considering to get one for myself again.
I used it for direct recording once, very nice results.
One precaution, the preamp adds a bit of growl to your sound, depending on bass, it would be safer to try it first.
I have boss bass limiter/enhancer - it changes the sound of my bass a lot, plus the compression is hard to adjust without any display or led.