To answer your specific question about the kernel proposed updates - the last main update for the kernel was v2.6.35-32.67. A slight increment was proposed at the end of March but was not pushed into the main repositories when the support date completed.

The change was relatively small - thus, unless you are looking for those specific fixes, I would stay with the stable and most widely tested kernel in the main repository.

Now that the support arrangements for maverick has been removed, the April 2012 archives is a good reference for the last remaining changes to maverick.

There can be a small number of proposed updates that miss the push to main - that is to be expected. If you look at the lp number [i.e. the launchpad reference] for the bug fix in question (look at the change log in update-manager), it usually gives a good indication how far it moved through the testing process before being pushed.

In summary - proposed repository was for testing. These updates did not complete their testing process before the support arrangements completed. You only need to update to specific packages if you were looking for a specific bug-fix that a proposed package may have contained.