I don't understand why you need to compensate for the sparseness of those areas. They're people just like I am. Land doesn't and shouldn't get its own say in the system.
Lets them participate in the game? They could still participate if they had an equal voice. Their weight on the national stage wouldn't be huge, since they're only 15% of the population, but getting 15% of the voice for 15% of the population seems fair to me. The rural population is similar in size to the black population. Should we give black people a disproportionate vote so they can better participate on the national stage?
I think the problem with rural areas is not their overly great political influence but rather the fact that they have been abandoned by mainstream politicians.