Normally, I don’t particularly notice the use of “ladies”
EXCEPT
Sometimes a young male waiter will refer to my all-female party as “ladies” in a certain tone of voice and that just absolutely makes me wince. As you say in the OP–"“oh please, that’s so smarmy/pretend-polite.” I hate it. It’s like he thinks it’s cute that women are out together or something.
As for “gals,” well that’s just a weird word. “Gals” makes me think of middle-aged ladies doing charity work or something. (Hey, I just used the word “ladies!”) Anyway, around here, the word “guys” can be used in a gender-neutral way.
Yikes! You’ll most likely get as many opinions as posts. My upbringing was So Cal. My gramma was southern Texan, ruled with an iron fist and taught my momma (and us grandchildren)manners, tyvm. 
All females may be referred to as “women”
Lady is a woman of class, taught manners - only cross your legs at the ankle, keep your knees together. Elbows off the table when eating, etc., etc., etc.
So, a madam in a brothel is a “woman,” probably not a “lady.”
I grew up saying Yes’m or yes ma’am to my mother and grandmother, and it was out of respect for them. Yes’m being the shortened version of yes ma’am or yes Mom. Madam was definitely a no-no, as it implied a woman in a brothel, unless being used as in Madam Chair, etc.
I detest being called “babe” or “broad” - however I think a lot of the preferences you see posted are age-related. A 20 year old was definitely reared in a whole different society than a 40 or 50 year old, so this, in my opinion, affects preference. I much prefer to be called Ladies, as opposed to girls when it implies youth - I am in my 40’s and don’t appreciate when someone treats me as if I were a young, inexperienced girl who doesn’t know anything. Context, therefore, affects my reaction.
That’s my 2 cents, and I’m stickin’ to it 
I prefer to be called “Miss,” rather than “Ma’am.” And I have no problem with “ladies,” or “guys.” I sometimes refer to my group of friends as “the girls,” so that’s not offensive either.
I have been surprised to be criticized over my use of “ladies” in what - in my mind - were innocuous contexts. Sort of “How are you ladies doing?”; “Good morning ladies!” type of way.
In my misquided old fogeyish way, I considered it a benign polite pleasantry. I even thought it connoted respect for one’s culture and manners, the same way “gentlemen” describes no male of my acquaintance.
I have been told by at least 3 women I can remember (including my wife!) that “lady” is insulting, demeaning, and I’m sure a number of other horrendous things. When I asked what term I was to use when addressing more than one woman, I was told I need not use any collective noun. I could simply say “How are you doing?”; “Good morning!”; etc.
Heck, it is a lot easier with guys. My buddies don’t care if you call us gebtlemen (never applicable) or assholes (unfortunately, too often the case.)
Instead of “guys” for mixed groups, I tend to say “folk.” As in, “Where do you folk want to go to dinner?”
I see the term “gal” as being used to describe a 50’s era cowgirl, as played by a fatally perky, cutsie Debbie Reynolds. You know, someone who’s forever annoying, that you don’t really have to take seriously. Guess that’s my objection to it. Otherwise, in regards to the OP, “ladies” doesn’t really bother me, as long as it’s not said (as previously mentioned) in some sort of snide, condescending way, although it does come across as a little school marm-ish overall. I do expect it though in a professional setting. “Girls” has an all-girls-school’s-sports-team feel to it, so that’s pretty benign. Plus, being from the south, I’m used to “ma’am” denoting respect, be it at 8 or 80. Therefore that’s ok too.
However, I absolutely LOATHE “broad”. Ick, ick, ick. Can’t stand “chick” either, if used in a derogatory sense; although in the kinda cute skaterboarder application is fine. “Miss”, as well as a singular “lady”, is just strange when applied to me, for I’m the last sort of person who needs to be described as such (shouts out to JuanitaTech!). And “madam” would just make me fall out in gales of laughter, pants wetting possibly ensuing.
But my undisputed favorite is the all-purpose “guys”. Love it! Definitely not gender specific in my, or most of my friend’s, book. I recommend that all of humanity should co-opt it for use. YMMV.
My problem is that I don’t know what to call my fellow teenagers! I think we’re too young to be “men” and “women” but it sounds childish to say “girls” and “boys”. But anyway, “ma’am” cracks me up because I’m not even an adult yet, and as for the other ones - well, I can’t remember anyone calling me “lady”, “broad”, “chick”, or “gal”, so it must not have bothered me if someone did. “Ladies” always makes me think of Strong Bad.