I just bought an Elliott Smith bootleg DVD for $18 (1 acoustic show, 1 show w/a band) and have to say it's some of the best money I've ever spent. Halfway through "Son of Sam" I realized I was totally losing it...what a talented son of a bitch. God I miss him.
The point of my post? Do what you want. It's only money. Not to be morbid, but the musicians on that stage will be dead and gone before you know it and so will we. It's a fact of life. Enjoy the Coldplay show. It's only money, and if you have eat ramen noodles for a week, so be it. If Chris Martin dies next year, you'll be glad you went and at least you can have the memories of having great seats. As for me, I saw Elliot 4 times (once with Heatmiser, once solo, twice with a band). I never even think about the money I spent because the memories I have are more valuable than the cash I spent.