It has been quite a long while since I owned my Walkabout. That is a unique sounding amp, and again, from my memory only, neither of these heads have quite the complexity and warmth of the Walkabout. However, the Streamliner would be the closer of the two, given its true tube preamp, and its wider voicing down low and up top. I would think that anyone who digs the Walkabout would also at least 'like' the streamliner. Those who LOVE the Walkabout (that head really has almost a cult following at this point, similar to the Walter Woods) will probably not consider this a 'no brainer, higher power' replacement.
This head has a lot of what makes the Walkabout great. Just like the passive tone control on a P Bass, there is a MASSIVE amount of tonal color that exists in this head by just varying the gain setting. I never found myself wanting to move the bass, mid or treble controls more than a touch off of center with the Streamliner. Similar with the Walkabout, I don't think I ever touched that semiparametric EQ section.... a subtle shift in the ratio of lows to mids, and different gain structure always got me to where I needed to go. So far, that is what I'm finding with the Streamliner.