I didn't use shades, but those are nice, especially if you sit in the car a lot (We don't.) There's a cover you can get for the carseat to keep it cool or you can throw a blanket over it. This is important because the metal pieced can get VERY HOT in the summer. I have actually burned my children with them before.
I didn't really use the mirrors either, but they can be helpful, especially if you let an older baby drink or eat in the car (they can choke, this is not advisable but sometimes "necessary," thereby requiring mirrors.) If you have a healthy baby, mirrors are not typically important except for your own peace of mind.
Having four low weight babies (4,5,6,7 lbs) I learned some things with #1 in the NICU that was great for newborns.
First of all, many carseats at the time had the crotch strap practically at the feet! That was not permitted to use with NICU babies and I had to buy a new carseat that had the strap 5 inches from the back of the seat. Some seats have them adjustable, at 5 and 7 or so inches to be moved when the child grows. This is a great idea and my two newer seats have this.
Secondly, roll up receiving blankets and fold them to create supports in the carseat as follows:
1) around the crotch strap, to rest between the baby's legs. This props the baby up if he is smaller and sloutches a bit in the seat. The idea is that you want his little bottom to sit firmly in the crease at the back of the seat. If it does without the blanket, you don't need it. This helps keep his airway clear so he can breathe well.
2) although I had the typical store bought support around the head, they showed me to line up a rolled receiving blanket on either side of the baby, and this also served to hold the baby in place.
I used this method even with my 7 lb baby for the first few weeks.
For future carseat safety, don't let moms convince you to move the baby forward facing early just because the law doesn't require it. The baby should be rear facing AT LEAST to 20 lbs AND 1 year. If possible get a carseat that lasts longer then 20 lbs. My Britax Blvd goes rear facing to 35 lbs! Also, don't take her out of the harness early (many moms are doing it at 3 years old.) She should be in a harness until AT LEAST 4 years AND 40 lbs. But if possible, go longer. That same Britax seat goes to 65 lbs forward facing in the harness!
My olders are in other Britax seats that are not suitable for a baby under 1. Regent I believe is 1 year/20 lbs to 80 lbs in harness. Frontier is 2 years/25 lbs to 80 lbs in harness and 100 lbs in vehicle seat belt. The manufacturer has the exp date of these seats at 9 years so they should be good for the full intended use (unless seat laws change, which isn't likely to happen excluding these particular seats as Britax have always been much more secure then the laws have required.)
S., mom to 4 preemie girls and due a boy THIS WEEK!!!!