Many of the Mitsubishis have what is known as an interference engine. That means if the timing belt were to break the pistons will hit (interfere with) the valves and the valves will be bent. The expense of replacing a cylinder head AND timing belt far exceeds the cost of replacing the timing belt as a preventative maintenance item. Just because you never heard of it, doesn’t mean it’s not a good idea. Here: http://www.gates.com/downloads/download_common.cfm?file=428-1466_web1.pdf&folder=brochure is a link to the Gates timing belt replacement guide. You didn’t say which Mitsu you own, so look yours up. If it says it should be replaced every 60K miles, do it.
You should also consider having it done by a good independent shop. It’s not rocket surgery. Any good mechanic can do it, probalby cheaper than the dealer. Ask around.