Michael,

The Amel original insulation is marginal at best, pretty much ANYTHING you do will be better. We rebuilt one of our settee freezers from scratch and used Panasonic vacuum panels.  The end result was the single greatest thing we have done to reduce our power consumption on Harmonie.  Down about 50% on that freezer, about 20% on our overall power draw, and no more warm corners inside the box. Just as important to the improvement was the proper double gasket seal on the lid.  The amount of ice we accumulate on the evaporator panel has decreased drastically.

The Panasonic U-Vacua panels are a bit complicated to work with, since they come in a limited selection of sizes, but were surprisingly low in cost.  I needed to design and build a complete new box to accommodate them.  Ended up not 100% vacuum insulated, but very close.  A big project, but we ended up with a significantly larger interior volume, and a better performing freezer.  

I had looked at aerogel, but ended up with the vacuum panels because they were lower cost per square foot of box at the same R-value, and I just had to put more time and brainpower in to the design of the box to accommodate them. Other people's decisions might be in a different place on that balance.

Don't count on disassembling the existing box, removing insulation and putting it back.  It was not made to come apart. Also, adding insulation, even really good insulation, to the outside of the existing box won't help all that much. At least in our case, after 25 years of nearly constant use, the existing poured foam was quite saturated with condensed water.

Bill Kinney
SM160, Harmonie
Simpson Bay, Sint Maarten