Rich people have the same number of seconds per day as poor people, except each second is worth more. Right now everyone is driving a black Model-T; there isn't a premium edition of email available, though one is certainly desired (personal assistants and secretaries currently fill this gap).

If the cost of a premium email/task-list system is less than the dollars saved in time, and less than an assistant, people will buy it. Aim for the higher-end market, solve their problems first on their dollar, and later expand downward to everyone else.