There's a difference between gold digging and being attracted to more successful men, in that gold digging is motivated by a conscious incentive to expend the man's economic resources. Unemployed men living in their mother's basements are unattractive compared to, say, machinists, who are in turn less attractive than doctors, but it's less a matter of golddigging and more a matter of social status and respectability. There's probably diminishing returns in the range between machinist and doctor, with a step function down for unemployed slackers and a step function up for multimillionaires.