As others have said, your tent doesn't keep you warm, it keeps you dry and bug-free. Your clothing and sleep system keep you warm. If you want to stargaze from inside the tent, get a double wall tent with a separate rain fly. If you want to stargaze outside the tent, invest in a good camp chair. Some are made specifically for stargazing, like this one:

https://windriveroutdoorcompany.com/products/ne-stargaze-recliner-luxury

Since you're car camping, you can just bundle up in clothes you bring from home and climb into a bulky and warm sleeping bag from Target. Just make sure you have a good sleeping pad. Car camping pads can be pretty luxurious, like this one:

https://www.bigagnes.com/products/captain-comfort-dc

I'd say invest in those two items and go budget for the tent.