I have Nav with Remote Touch on the RX as the family hauler/trip vehicle, but on the IS, the additional cost (over 3500$ - 6000K$ in Canada depending on package
) was not justified for me as my daily driver to work. The rare time I need to drive to an unknown destination, I pull out my 100$ Garmin and I'm good.
The US version has Enform which provides access to cool apps via your smartphone as well as subscription-free live traffic and weather. It is also a cheaper and standalone option if I'm not mistaken. The Canadian Nav lacks these features which makes the value proposition poor in my opinion
if you don't care much for the other features in the packages like moonroof, memory seats, etc.
The Standard Audio Display (and Controller) has high-res graphics (just like the Nav version) giving you nice graphical displays on your music artists/albums, fuel economy graphs, HVAC controls, etc. Almost all the same functions as the Nav version, minus the Nav basically (in Canada). As for voice controls all essentials are there with the standard system minus nav-specific control: You can place phone calls by number or from your phone's address book by simply saying "call John Smith" (it has great voice-recognition); you can hear incoming texts and reply back, and a few other voice control functions related to music control.
As for ergonomics, the round **** works well and is intuitive and equally as effective as the Remote Touch Controller (from experience with my RX). The round **** behaves more like the German systems where you rotate the **** or push up/right/left/down to move your cursor, and push down to enter and select, whereas the remote touch is more mouse-like in movement. However, I find myself using the steering wheel mounted controls mostly as it's in easier reach for both the IS and the RX.
A final worthy incentive with the non-Nav, is the tray. This is a great spot to put your phone.
Since you're Canadian (Nova Scotia), personally, in summary, if you're budget conscious and don't need nav and the other packaged features, skip it. The standard Audio Display is so nicely crafted, operates well, and looks so slick, it exudes a premium look and feel (See pics below)
If you were shopping for an ES or RX for that matter, the non-Nav displays are horrible black/white 80s LCD display that looks out of place in Lexus. In those cars I definitely would spend the extra cash on the Nav packages just for the look. Hope this helps. Good luck.