I've always disliked this part...

Thieves are able to hide on roads and Rangers are not.

As a soldier I think I am qualified to say that Ambushes most often occur along roads, trails, and natural lines of drift (Streams, gorges, easily passed areas.)

Thieves being able to sneak on roads has always bothered me but hey game balance I suppose.

I've always pictured rangers creeping along the roads and ambushing.

My thoughts, Make thieves uber nasty in cities and less effective out of them similar to rangers in woods. I.E. Put some lags on their skills for staying to long out of their element.

I'd also like to see Invisibility detects become harder to obtain.

And I'm spent!