Limited lifespans have nothing to do with resource constraints. There is just nothing to select for longer lifespans beyond the time it takes to reproduce.
Definitely there is. If humans spent a long time learning, and were more productive and fruitful in their later years, developing more intelligent systems, they would theoretically out-compete a civilization that wasn't able to develop such advanced skills and learning - especially related to passing on information.
The missing issue not obvious in genes is the amount of cultural information and learning passed on. A genetically 'superior' race of beings (faster, smarter, more disease resistant) would surely be 'beaten' by a group of lesser beings who were able to cooperate, learn, cognize, master tools, pass on wisdom etc...