Well, I guess I will be different here and give an argument for the exhaust.
If you are just street driving your car while doing modifications as you can afford them then a saggy suspension you can deal with. You already know how it handles and will react to your inputs so you can drive accordingly.
If you have an exhaust system that is going to start to get worse it can do that without you knowing. Exhaust fumes can sneak up on you and the next thing you know you are blacking out and running off the road or worse into oncoming traffic.
Believe me I have investigated crashes where this scenario has happened.
I know, there is always someone who thinks SAFETY FIRST....
Tom