My thought is this issue should probably be addressed from time to time and since last list was in November, I thought a reminder/update appropriate:

Awesome !!! Darn your good,lol, lol & thank you for the info & much appreciated.
So for The Palace Station a key is required  to activate the elevator for the main remodeled rooms, as for The Garden Rooms (with no view of a garden) that are still outdated  set way in the back with a free cardio work out included in your day & a doozy to find them, no key is required  
Also The Palms Place the condos next  to The Palms- no key is required & no security.  
Aliante-  no key or security  
Four Seasons - did not require a key recently (Jan) perhaps security was out to lunch lo

keys required and key checked because:

I was staying at the Hilton Grand Vacations next to Circus Circus and afetr 8pm you need to show id that you're staying there or card key or they will not let you in.

I just left the Cosmo and I didn't need a key to get up.  West Tower

I can confirm the elevators at the main tower at the palace station require a key. You may have to slide the key in and out ten times to get it to work, but eventually it will work haha. I have always stayed there in the past, but when I come out in a couple of months I am treating myself this time with a lake view suite at Vdara.  

Lately I have had the same experience. Maybe they disabled the key control on the elevators

There are not any Lake view rooms at the Vdara.

the east tower you need a key to get up the west tower you don't...  

to correct and improve the list.  I intended to make a reply to posting the list indicating I wanted folks make such comments, but after waiting a couple of hours, it was past my bedtime.  I will make adjustments as people give me information.

I was there about 3 months or so ago and I didn't need a key and there wasn't security.  I went right up.  I don't remember the exact day (weekday or weekend) but it was at night after like 9pm or something like that.

It is something I have thought about.  My basic reason for lumping the two together is that it requires the hobbyist, or provider hosting incall, to come down from the room to greet their guest.

Fantastic suites.
Very cool, relaxing and no casino or smoking

Hilton Suites on North Strip require key

This is really helpful information. Unfortunately almost all hotels that I like are on the top of your list. What I am mostly concerned about is if one ever gets stopped to get the IDs checked. Recently I stayed at Bellagio and took up 3 providers within one day. I got worried that they would stop me at some point. Is this fear real?

3 in one day!?! Congratulations, nice to be young.  It now takes me all night to do what I used to do all night.

I stayed at both Silver Sevens (formerly Terribles) and the Hard Rock during avns 2 weeks ago.

Silver Sevens - no key card required, no security at the elevators

Hard Rock - I stayed in the Paradise Tower, there is a key card slot in the elevators (for the lower floors) leading to those rooms (I stayed on the 7th floor) but the elevator still moved up and down w/out my room key card. There was security at the enterance ways to those elevators but they werent there all the time & it was only because it was avns.

Treasure Island security is random, while walking through taking a shortcut from the Wynn to the Mirage recently, security was checking elevators at noon!

I stayed at the Trump in June, and they checked Key cards after 9 pm, security by entrance to elevator alcove.