Never tried the $20 trick myself.

To me staying in a lake view room is good enough.

The views from those rooms are amazing IMO.

I have been lucky enough to stay in them a couple of times.

You can at least try. You have nothing to lose, and you might gain.

I've done this at the Luxor (before it went down hill), MGM, and Man Bay. Try it. Worst case, they say they can't do it.

I have tried it twice at cosmo. First time I got a nice upgrade  with a " summer essentials" near the cabana rental thrown in. Second time, they were really busy( completely booked), and the front desk guy tried with no success and wanted to give my $20 back, but I told him to keep it anyways. And the next day, he called me and moved me to the higher suite with a fantastic view once it became available, though I was not expecting it. So $20 goes a long way it seems. No harm in trying.

Yes it works at Bellagio.  No need to say anything, just put the bill between the license and credit card.  An attentive clerk will tell you what they were able to do for you.  If they can't (heavy occupancy) they will be apologetic.  Let them keep the $20, it was a tip not a bribe

Same as with the ladies, treat them with respect and the experience will be better.

I would try and select a Front Desk clerk who is checking people in alone.
Avoid anyone who looks to be in training. Recently trained employees will not be aware of the "trick".

The very young, good looking blonde may not be the best person to check you in. I have tried 3 times ( 1 success, 1 failure and 1 story)

If you have players card and have a higher level (like Gold at Palazzo, platinum at Cosmo etc.) they usually automatically upgrade you; but it always help to be nice.

if it is a Sunday or weekday checkin, definitely try, but weekends area little tricky.

you are already fully comped for a regular room?  Would an upgrade affect the comp?  Or be perceived as an attempt to take advantage of your host, who has already established your room "level?"