Hi, this is an way out of the box idea:
In order to reduce HTTP Requests somehow, someway plugins and their respected developers, whose contributions I really do admire, should be encouraged to either:
a) Use an universal css file that satisifies 90% of their design and creative needs. It could include elements for styling common features like donation boxes, settings etc.. That universal css file can in return be changed and styled by the end-user of WordPress, if desired.
b)Make all of their css easily movable to the core and central css file of the selected theme.