Any sort of vacuum retard at low speed running is for emissions only (reduces NOx). You should be able to eliminate it without any ill effects. Turbo engines under load obviously benefit from ignition retard.

.... and it goes without saying that you would need to set your timing at idle to about 11 degrees BTDC instead of the specified 5 degrees ATDC to achieve 29 degrees BTDC at 4k rpm if you disconnect and plug the vacuum advance (in my case anyway).