On the 900 equipment it looks as if the default power level is 24 dBm. Does anyone ever adjust this? Like turning it up to 26 or 28 to help in getting people that might be just on the threshold of getting a signal.
This settings adjusts how much power is sent to the antenna. Most countries regulate transmitter output power: in the US, the FCC sets this limit to 4 watts (or 36 dB).
To operate within the bounds of the law, you need to set this to:
max power level (dB) - antenna gain (dB) = transmitter output power (dB)
So essentially on the 900 MHz APs 24 is the highest it can go?
Again, depends on the antenna.
If you have an 8dB antenna, then the max power would be
36dB Max power - 8dB antenna gain = 28dB
You can fudge this a few dB to compensate for cable and connector losses.