Well I can't argue many of those points because i'm certainly not an expert; However, I will say that I don't believe a gamer can be either "average" or "hardcore" as i've found that either or will frequently meld the two or dedicate a certain attitude to a specific game. Everquest for example is something I used to be very "hardcore" about but at the same time I played many arcade based games on xbox live frivolously and without care. Lately i've been wholly consumed by Call of Duty 4, yet I go back to Doom on xbox live to spray and pray every other day.
I suppose if I had to consider a specific market as you mentioned I would target the "masses" and use the "easy to learn, difficult to master" style of gameplay in order to possibly draw in the "hardcore" gamers as well. I don't understand why a game can only target one crowd.