There are route specific campaigns, they do what you need, increase RI only for a selected route. You need it only if you want to get to RI 100 sooner than without such a campaign.
Once you get to RI 100, it does not matter where is your general campaign based, you just need to maintain CI at decent level, regardless of what general campaigns are activated.
Now, what is a decent CI, I read several opinions, and it seems to be around 60. As you grow, marketing cost will become irrelevant so you will want to go for CI 100 as well, just for the sake of rank, but for the sake of load factor, CI 60 seems to do the job quite well.