I am in the process of completing my second ecommerce site, (first in php) and have learned a lot recently, which is needed to round out ecart.
Key topics such as
preventing customers adding more to the cart than you have in stock
managing paypal ipn
tailoring voucher/discount code to allow database updating etc etc
have all been things i have learned to do by browsing through the forums and picking up tips
a 'how to' forum would not only be good for other users, but those posting (such as myself) may find better ways of achieving their goals
Could we not do all this in the new Power Store forum?
It seems the logical place to post all the items you mention!