Could you provide the dmesg output on a txt file? In that way we could have a better picture of the issue. Something else you can try is a fresh install of the SD card image, since something might got corrupted.
I am also on the 0.7.5 image and the official release board firmware. I am getting intermittent crashes relating to the wifi. I've searched for a solution but haven't seen similar issues so am wondering if it is something between my nic and router, or a OS/driver/firmware error or a hw problem. The console output I get when a crash happens is:
root@clanton:~# [ 2383.820236] iwlwifi 0000:01:00.0: fail to
flush all tx fifo queues
[ 2385.850265] iwlwifi 0000:01:00.0: Error sending
REPLY_ADD_STA: time out after 2000ms.
[ 2385.858274] iwlwifi 0000:01:00.0: Current CMD queue
read_ptr 85 write_ptr 88
[ 2385.867444] wlan0: failed to remove key (0,
00:24:a1:76:03:13) from hardware (-110)
[ 2387.870258] iwlwifi 0000:01:00.0: Error sending
REPLY_QOS_PARAM: time out after 2000ms.
[ 2387.878435] iwlwifi 0000:01:00.0: Current CMD queue
read_ptr 85 write_ptr 91
[ 2387.885891] iwlwifi 0000:01:00.0: Failed to update QoS
[ 2388.959471] iwlwifi 0000:01:00.0: ACTIVATE a non DRIVER
active station id 0 addr 00:24:a1:76:03:13
[ 2388.968612] iwlwifi 0000:01:00.0: HCMD_ACTIVE already
clear for command REPLY_QOS_PARAM
[ 2388.969222] iwlwifi 0000:01:00.0: HCMD_ACTIVE already
clear for command REPLY_RXON
[ 2388.992833] cfg80211: Calling CRDA for country: US