I decided to answer my own question with the solution I found at least, not least because, while there are many similar questions (and answers) around for the Intel 2200BG chip, none concerned the acerhk module and Acer hardware.

The way I solved this is by installing the acerhk module. This Hotkeys module also controls the function of the wireless hardware switch.
This module was removed in a previous release (9.10?) which is probably why the hardware switch stopped working in the first place. Even the source package was removed from the standard repositories a while back. Luckily, I found a recent version on Launchpad, including a PPA.

1) Install acerhk-source:

sudo add-apt-repository ppa:cogito-16/ppa

sudo apt-get update

sudo apt-get install acerhk-source

2) Like the README.Debian in usr/share/doc/acerhk-source says, do

sudo module-assistant auto-install acerhk

3) Load the module according to your model in this rfswitch.SF model matrix. For me, this was

sudo modprobe acerhk force_series=290 usedritek=1 verbose=1

sudo echo 1 > /proc/driver/acerhk/wirelessled

This will to everything you need. Your wireless hardware switch should work now.

4) To make this change permanent after reboot, you have to do as explained here:

Create the config file
echo 'options acerhk force_series=290 usedritek=1 verbose=1' | sudo tee /etc/modprobe.d/acerhk.conf

Edit /etc/rc.local

echo 1 > /proc/driver/acerhk/wirelessled

exit0

and /etc/modules as root an add an entry for the module

acerhk

When I think this has stumped me for >1 year (I don't use this laptop very often anymore), and I probably wasted 2+ solid days searching for a solution, it was pretty simple in the end. I hope this will help you, too.

NB: You can also get acerhk source from its homepage, but this didn't compile for me with the current kernel - make just sat there and did nothing, probably the reason why it got kicked out of the standard repos.