Hello, I have a old Canon 450D and some of the focus point is spoiled, can focus but no more light because last them when I first bought it I open it and wipe it with cloth when have mist inside the camera

If it doesn't bother me should I fix it?

I want to use it for shooting aurora but I'm using the most basic lens only, I'm wondering can I still buy lens for this model dslr?

Should I buy lens and fix the camera or just buy a new dslr? but I won't use it very often just for shooting aurora only, other than that, would prefer using phone camera because easier to bring.

Thank you everyone, have old camera but newbie on dslr here