Your Mk I is more than adequate for your 2-3 times a year use, especially as you think it sharp enough. Why don't you donate the price of the Mk II to a suitable charity, like one for ebola, instead. Think of the satisfaction you will get from that. You could also sell off your unused lenses and donate the cash raised for a worthy charity as well. It will cure your GAS and do some good.
Not to be a dissenter, but it is easy to be charitable with other people's money. Why don't you sell your Mercedes and buy a nice Honda coup, and give the difference to xyz... easy answer, because I don't want to.