I don't think you'd need anywhere near 18K to freshen your car to like new, Gogogwen.
I just got one of these, and with 70,000 miles it seems like a new car to me.
If you have a few thousand to spend you can take it to a good mechanic and have all the suspension pieces and bushings checked and replaced if worn, maybe a couple new hubs on the front end, brakes all around (also gets you new brake fluid, which makes all the difference), new coolant and flushed, heck, change the thermostat (cheap), belt, and tires. To go first class have the A/C serviced and the transmission serviced and fluid changed.
The engines can run apparently forever. If you aren't a play racer and screaming around at high RPM your engine is probably fine.
Do all this and the car would be like new.

Then again, $7,000 will buy a very nice HHR with lower miles. I saw one with 28,000 on it, but it wasn't in my area.