Report to compare two budgets?
Found at:
Quicken will do that for the user; either automatically when the current system date is in a later year than the most current budget displayed in Quicken, or automatically when the user clicks the right-pointing Budget year arrow when the budget for the current year is displayed.
" ... and then going through and tweaking most of the values."
Once Quicken has automatically created the new year budget, the user can "tweak" any of those automatically created budget values.
But the op's real interest is " ... to run a report or do a comparison of the difference between the new budget and the previous one."
There is no Quicken report that will do that.
But it is possible to export a budget (a budget year) to a tab-delimited text file that can be opened (or imported) into Excel. The user can create a separate tab-delimited text file for each budget, then import those two files into Excel (importing the second one below the first, so their monthly columns are aligned).
At that point it is a fairly trivial matter to visually compare the two budgets.
If the user wants the differences computed, they should be able to utilize Excel features to accomplish that.