I'm no flooring expert but when we put hardwood on the 2nd floor of our home we put a special padding underneath to buffer sound and cushion it some. It's helped a great deal to reduce echo and noise. Still, if someone goes tromping through at a fast clip some of the pieces in my hutch will vibrate a little. Very slight. Large area rugs can help reduce noise and vibration, too.

Plus the flooring forum here might be able to help. We had some floor boards below our kitchen subfloor that were getting loose and creaky, but that was easy access via the basement to put new screws in the joists to tighten all that up again (some can work loose over time with use). Tho I know that's not easy access for you, it might be something simple like that. My point is I wouldn't worry about the floor collapsing, you'd really feel instability under your feet walking on that.

If the budget's tight check big box stores for carpet area rugs, they have some decent ones that don't cost an arm and a leg. Some of my tenants are using those over hardwood in one house. Looks nice and I think it was under $30 for 6x8 or 8x10 with finished edges.