Dont like the idea of #2...... again its manual.
I would think the best way would be to have a token that triggers the update, then have that token on the main areas where quotas are more important - the main index page of a skin for domain admins and other importantn pages such as 'site information' pages for admins and resellers.
With the other pages i cant see it being to important, usually when you go into the add new skins page your not looking for users quotas, so you would therefore not need to slow down the panel updating quotas.
With the token, if it was possible it allows the different kinds of skins to utilising a feature without dramatic chnages in speed.... since it would only be one or 2 pages affected at all.
Once scripting is enabled within skins that idea would only need to be once even.. which would increase the speed even further.
Chris