Just got my Avengers Pro a couple of months ago and wanted jump in on this thread - hoping there are more Avengers owners out there who are willing to share more tweaks!

So far, the only tweak I've made is to put Loctite Blue (the non-permanent kind) on the hex screws holding down the tesseract to the plate. One of the screws was often getting loose, causing the plate under the tesseract to tilt and often trap balls that were rolling slowly over it.

The third ball after getting the Loki lock is also getting stuck on the upper right hand lane, where the metal ramp meets the clear vertical plastic - might be a matter for adjusting the leveling,

Also, this is more of a mod than a tweak, but I installed the Pinball Refinery's tesseract mod v2:
http://pinballrefinery.com/store#!/~/product/category=4502268&id=19335862

The Pinball Refinery cube looks much, much better than stock, and the blue LED lighting on the cube making it glow is fantastic, if very bright.