I'd agree that it's worth considering a more recent model, unless you really need a model that Peter Snell himself designed.
The models designed by Kevin Voecks, like your J/IV, were very, very well reviewed by Stereophile magazine. In particular, the Type D, which I own and love, and the C/V, which recieve numerous glowing remarks on this board, are both astounding used speaker values. Both models often sell in the $1000 or less range with the D's occasionally dipping into the $600 range.
A set of Type D's is on sale on this board now for $800 -> http://www.audiogon.com/cgi-bin/cls.pl?spkrfull&1275012004
You really should try to give the Type D's and Type C/V's a listen.
The bass goes very low on both. Don't forget that Snell was very strict with frequency response measurements. They used an anechoic chamber and limited their published numbers to usually +/- 2dB (sometimes less!), which is not the industry norm. The Type D was listed as 36Hz to 20kHz +/- 1.75dB anechoic. Stereophile's testing revealed them to be good to "at least 30Hz". The C/V's went even lower.
Finally, the old Snell specifications page that can be found via Google and was posted by Snell several years back contains several incorrect entries, those specifications can not be used reliably.