@Gztk: Difference is, that in hardcore mode, you don't loose any army after succesful defence or attack, even in situation where rolls are almost the same.
@COJlucian: I didn't check it with lvl 3 antivirus yet, but selling damaged Antivir lvl 2 then buying new one and upgrading it should be still cheaper.
I'll show this with most typical price set : 150$ for buying, 400$ for upgrading
fixing: 400$
selling and buying a new one: 150+400-200=350$
I'm sure they are, in some shady corners of the internet.