Thanks for the replies, I ended up ordering the AVT-871. I hope it can make much better captures but I have my doubts.
While waiting for it to arrive I experimented with trying to use software to to correct the jitter. Most of the AviSynth scripts I found do a poor job though.
I was able to get pretty good results with a modified version of vcmohan's de-jitter plug-in
that I made. It seems to work in about 95% of my captured videos. I adapted the plug-in to do the following:
1. Do standard edge threshold detection.
2. Take a weighted average of all the preceding pixel's luma.
3. Average shift amounts from x# of lines before & after.
4. Results is a floating point shift number such as 1.12345.
Take proportional ratios of adjacent "pixels" from shift distance.
For Example if shift is 1.75: px1 = 0.25*px2 + 0.75*px3
I find this method produced much more smooth shifting without any jarring shifts or false positives by noise.
Attached is a 2x magnification of the bottom of a VHS capture before and after my filter. maxDist: 10, thresh: 30, Avg: 3, Padding: 40, blend: true