From a pure RSSI standpoint, those signals are right in the sweet spot for most designs. I'd hazard a guess that signal strength isn't the main culprit with the reported issues.
If this was a greenfield design at 30 feet, I'd lean towards a patch or maybe a downtilt Omni depending on the building layout. You really should do an AP on a stick survey though to validate the antenna choice.
Raising the AP power will almost always cause more problems.
Installing omni antennas at a large height (over 3-4 meters) is not recommended.
Choise of antennas and installation height should be done at least with a simulation and later verified on-site.
You probably have a few APs installed in the same area and you are seeing most of them due to the antenna's and height used. Patch antennas can be used to localize each APs coverage area and reduce signal overlap between APs, but you will need more APs.
I often use MA-ANT-3-E6 antennes to cover ground areas if the ceiling is above 8m (in designs). Below that I'd advise you to use a downtilt omni antenna. Main advantage of the 3-E is that you get a smaller coverage cell than with an omni so if roaming is required this will give you a more predictable wireless environment.
This is a MR42E with a 3-E antennes at approx 11m in a warehouse. 3-F antennes are used for getting the signal between the racks (also mounted at 11m) and standard APs at the docks (mounted at 3m).