Thanks for all your helpful suggestions. I was trying to avoid looking at each hotel individually, and I've found exactly what I was looking for, but it wasn't on the Marriott Rewards website. Until now, I've only heard Tuggers mention Flyertalk and never looked at it myself, but I thought I would give that a try. That's where I found a list of concierge lounges that were open on weekends that was evidently compiled a few years ago. It has a disclaimer at the top stating that Marriott has significantly downgraded this perk, but, in any case, there exists a list of participating Marriotts.
I started this thread asking about lounges, and I know this is somewhat unrelated, but now I'm interested in learning more about concierge levels. What exactly are the different concierge levels? Some hotels say 1, 2 or 3 levels. How does that work? Does room availability change or is it constant? In other words, do they have blackout dates when there is no availability?
Also, the selection of available rooms changes depending upon whether I search with points or cash. Why are some rooms only available with one and not the other?
Sorry for so many newbie questions, but until now, I've just accumulated points and never used them.