I wondered about this. If you already do the hardest difficulty for weekly strikes it doesnt matter to you but for those of us who just do the normal difficulty. if you start from Hard, and work to very hard each run will net you 3 coins. If you just do Very Hard, that is a straight 9 coins. So it is possible to get 9 coins on one character from Heroic Strikes. I guess your characters inventory is also interchangeable, so having alts will benefit you even more when building up your strange coin collection.