I am getting a new speaker system but the speaker system is going to draw more power from my car, the current alternator is stock and I am not sure that it can handle it. I have yet to test if the alternator is in good shape, but the interior lights dim when I turn on my headlights. Should I get a new alternator that can support the extra power draw?
Yes. Load test your electrical system & you should figure out your alternator’s health easily.
Do you really need to play rock concerts in your 40yr old Cressida, though?
Sounds like you definitely need a new alternator with your symptoms. I always bought remans for my '81 with a Limited Lifetime Warranty when I couldn't find an OEM unit.
Rock Auto has 2, 65 amp alternators for your car. That should be enough power for you to rupture your ear drums with some AC/DC.