I'm a skinny neck geek, and that I can tell, these are the two basses that come standard with the #8 neck (1.5, 12" radius, right?).

I like a lot of tonal variety, but I'm mainly interested in two sounds - a low-midrangey, punchy growl, and a cleaner, 'hi-fi' sound. I'm thinking that the ASAT is going to do a better job of giving me what I'm looking for, but (as well as more tonal options for the future) ... I'd love to hear more on the pros and cons on this.

Secondarily, it looks like I'm seeing used ASATs for about the same price as new with warranty JB2s - how much of a factor should I let that be?

I should mention, the heavier ASAT body doesn't bother me - I'm the odd sort who doesn't mind a heavier body in the slightest. I also like its shape - things that step outside of the two-horn norm are interesting to me.

ASAT will give you all the tonal options you'll need. SB-2 is another one to consider, but it won't do the hi-fi sound as well. Keep in mind that these are still bolt-on ash-bodied, maple-necked basses with passive pickups. They will not do the EMG zing or the Ken Smith shimmer. They will do a hi-fi version of the Fender sound, but you'll never mistake an ASAT for a Warwick Thumb.

ASAT has the same active switchable dual coil 'buckers as an L2000, the JB2 is-essentailly-as Fender Jazz clone.
Very different from each other.

ASAT has the same active switchable dual coil 'buckers as an L2000, the JB2 is-essentailly-as Fender Jazz clone.
Very different from each other.

Apologies for a semi-hi-jack here. I have an L2000 and it's really the only bass I've ever played. I don't have access to a JB-2, but I'm wondering specifically what would be the tonal and tactile differences?

I played a MIM Fender Jazz a few months ago and my take away was: thinner neck, lighter instrument, different--though hard to categorize--tone that was maybe slightly more gritty or woodsier? I'm kind of looking for something that sounds significantly different than the L2000 (which is tough given the L2000's flexibility). I love the look of the JB-2, I love the G&L build quality, and someone's got one for sale over in the classifieds! My other, cheaper option, is to get an SX jazz with a maple neck.

Thanks in advance for any thoughts (and I realize this is all subjective as hell).

Yessir, a JB2 is gonna be way different sonically than an L2000.
All my L2000's have big ass chunky necks, but I've made a point of that. The JB2 I have has a 1.5" nut width, and the it's deeper than your traditional Jazz. Nice neck. The only Fender Jazz I've had in a long time as a 62 re-issue. I find the JB2 cleaner, brighter, and not as deep as that particular instrument...

I bought a JB-2 last year off ebay and the neck I believe is the #8 neck (jazz neck). As a passive bass it sounds great, a bit old school. I also ordered an ASAT HB with a #8 neck last year. It plays great and the tonal variety is immense (of course, there's always the one tone that I'm looking for so that's the one that I dial in). I also liked the shape of the ASAT and that's one of the reasons I chose it over the L2k.

I really have no business buying another bass. The L2000 is plenty for what I need/do. I'm just having a bit of G.A.S. for that Jazz bass vibe/look, which I should satisfy with an SX, but I'm a sucker for quality and I know a JB-2 would be great. I think I just need to count to 10 and sleep on things a bit, then I'll probably wind up not buying anything.

That's probably wise. The money may be better spent on another amp to add to the collection. Or another cab. Or pedals. Or strings.

For those of you having trouble falling asleep at night wondering what I'd do:

http://www.talkbass.com/forum/showthread.php?t=310949

Seemed to be a moment of synchronicity.