This loss of connectivity is still happening; at least within my environment, it's quite reproducible. While I've eliminated the message about being unable to set the RTC to 1024Hz by recompiling my host kernel without CONFIG_HPET_RTC_IRQ, the host's kernel is frequently complaining "rtc: lost some interrupts at 1024Hz".
I'm using tap-based networking (-net nic -net tap,ifname=tap0,script=./tap0-start), where tap0 is bridged to my local ethernet device, and outgoing network traffic from the qemu instance is visible if I monitor traffic on the bridge. Indeed, external responses to such traffic (ie. ARP responses) are visible on the bridge, but evidently not to the virtual machine: the TX counter rises when I try to ping the outside world, but the RX counter does not. Resetting the device (ifconfig eth0 down; ifconfig eth0 up) brings it back alive -- but this isn't an action which can trivially be slotted into a trivial, single-threaded install script. These same scripts have been tested on real hardware, and have not turned up this issue. Certainly, a race condition unrelated to qemu is possible, but I'd appreciate any insight 'yall can provide. Thank you!