You never said so, but I am assuming that the cars you have looked at are automatics.
I understand your feeling about your car getting older, mine is the same way. It gave trouble yesterday, no big deal, just put a fuel filter in and it fixed it up. I hit a deer a couple of months ago and it mashed in the passenger side door, I removed the door panel and pushed it out and it looks reasonable. I need to put a windshield in it and it needs front rotors, they're warped.
My A/C is still perfect, I hold my breath every spring, but it's hanging on.
I see 300E's for sale in the North Dallas area all the time, and I'm sure I could spend 5 or 6 k and get one in much better shape, but what keeps me from doing that is my manual transmission. It took several years to find it and I'm determined to keep it going.
IMHO on a scale of 1 to 10 a 300E is a 7, but a 300E with a manual transmission is a perfect 10. It's all about taste and what I want in a car.
I'm driving it A LOT right now, and basically using it up, but I really enjoy driving it.
Best of luck with your decision,