Regarding the sale of IP, yes selling it will 'shrink' your influence circle. The opposite is true, buy enough and your influence area can go up. Second that about the UP, basically you are buying and selling votes. Another tactic I employ as well as demanding all a race's cash for peace, I will also demand as much IP as I can get. That is, if they are sueing me for peace and I don't want to fool with them atm.
Sometimes the numbers have to be huge. For instance 9000 IP is enough to notice a shrink. Minor races don't have an 'aura' on the mini-map.
You can never have enough UP, there'll always be something come along thats worth voting down. Like sharing 5% of your income with each race.