I suspect that opinions vary so widely on the Sansamp, when used as a pedal/stompbox, not only because of differences in the tones we prefer but because we are all using it with different rigs and different basses. As someone noted previously, it is designed to emulate the (miked) sound of a fat tube amp through a cabinet -- mainly for use when recording direct (i.e., sans amp and cab). When such a signal then is processed by another preamp, power amp, and cabinet, the results will vary greatly depending on the rig. And, I think, the bass you happen to be playing too.
For example, I used to use my Sansamp all the time through my old Ampeg B-2 combo w/ 15" speaker, with all of my basses. I thought it made my rig sound like a fat SVT tube amp through an Ampeg 8x10. Then I added a (relatively bright-sounding) Avatar 2x10 extension cab, and I didn't like the Sansamp with that setup nearly as much -- except when playing my Carvin LB70. Then I picked up a more portable Ampeg B100R, which already does a great tube-emulation thing and thus sounds terrible with the Sansamp. (Department of Redundancy Department?) Then I bought a Jack Casady sig, which has incredibly rich, complex mids, and the Sansamp "sucks out the mids" as stated by the O.P. I can almost get them back by tweaking the Sansamp settings as discussed above, but on balance the JC sounds better without it. (BUT, it sounds amazing through a real tube amp, so go figure.)
Anyway, the point is that some people are all about "Sansamp sucks" and others are all about "Sansamp rocks," but both are true depending on your rig (and, of course, your taste).