Azimuth: how critical is it?

What makes you say your azimuth is "slightly off"? Is the headshell not parallel to the platter surface, when viewed from head on?
Simao, Shims could be used on one side of the top of the cartridge, as a wedge between cartridge body and headshell undersurface, to correct for azimuth. Perhaps that is the intent.

The thing about having azimuth adjustable via the tonearm is that it also affords the user the opportunity to get it wrong.  As MC suggests, very often adjusting the cartridge body at an angle to the LP surface, in order to optimize the electrical readouts of channel crosstalk and phase, will also sit your stylus tip at a subotimal angle to the groove walls as regards its physical contact patches.  This is "not good", because it leads to uneven stylus wear and distortions that may be more noticeable than suboptimal crosstalk or phase anomalies.  I do own 2-3 tonearms that permit easy azimuth adjustment, but in recent years, I have settled on the paramount importance of having the stylus sit "square" to the groove walls, over all else. 

But if your headshell is fixed at an angle other than parallel to the LP surface when viewed from the front, I would suggest doing something simple to fix that and then stop worrying.

Also, if you look on Soundsmith and study well you will see Peter Ledermann came up with an ingenious solution that enables all his cartridges to have azimuth adjustment regardless of what arm they are used on. When you see how it works you will realize you can do the exact same thing yourself. Simply place a round toothpick along the center line between the cartridge and the head shell. Then by adjusting the screws you will be able to rock the cartridge one way or the other and wala, azimuth adjustment! 

Looking at the headshell head on there is a slight visible tilt, maybe 3 - 5 degrees visually.  I do not have measurement devices to check cross talk, etc.

The sound is good to very good, with good imaging.  My particular listening situation is a little compromised by the use of the listening space also as a family/great room.  My wife tolerates it, kinda.

3 to 5 degrees is not trivial.  Take a look at MC's reference to Peter Lederman's tooth pick trick, and maybe try it. Perhaps you will enjoy your sound even more, by a tiny bit.

Correct azimuth allows you to have a soundstage that, for many recordings, extends well beyond the speakers and well behind them. Since I listen to classical music, I think the rewards of a proper azimuth are large and rewarding. YMMV.

The adjustment is very easy with my arm.  I find that with the proper records, I can adjust it by ear. Some people use expensive devices to do so. I have read about them and I would find them a pain, and expensive pain at that.

Though others may differ, playing a mono record with one channel out of phase will get you very close, perhaps close enough.