My friend, I totally understand...
I told me wife nearly exactly what you posted... I'm concerned, anxious, feeling guilty, etc. Her response: "Honey, for 27 years, I've watched you struggle to get your career going, work endless hours, with months at a time away from home. I've watched you sacrifice everything you wanted in order to provide for your family. You've supported me and our two kids better than a wife could ever ask a husband to do. It's time you rewarded yourself for a job well done. Get the car, and enjoy every second of it. Don't feel bad, guilty or anxious. You've done your job for me and our family. I want you to get that car and enjoy every minute of it. Oh, and I want you to take me to a drive in theater after we get the car. And make out. A lot."
Life is short. Do something that makes you happy, even if it means you have to stretch a bit to do it. Yeah, "Life is short" gets used a lot, but often time people don't really realize how much that really applies; I've had several friends have their lives cut short recently and unexpectedly. Buy the car. Eat your desert. Be happy. Gawd knows you deserve it.
Chances are, you're the typical American man that has worked his whole life to support his family and has never bothered to pat himself on the back a bit for it.
Pat your back, man... you've done good.
Oh, and post pics of your new ride.