If the choice is between having an at least reasonably well defined genre or watering the genre down so much that nearly everything will fit... then I'd say go with the former.
Even though the latter would surely mean there would be a lot more 'adventure' games, what's the point if the games that make it up are different enough to have very little in common?
Let's just call every game an adventure game and we'll never have to worry about adventure games dying ever again
