I like the flexible ground straps as they are less likely to break with movement, like the hood or trunk lid. Look at a retired police car (not one in use) and you'll see lot's of extra grounds. If you don't need to move it a lot, a heavy wire will work. You just need continuity. Metal costs money and they wouldn't have put it there if you didn't need it. I'd put a little dielectric grease where it bolts to the battery or body to prevent corrosion. I'd check the heavy positive wire to the starter while you're in there. They usually don't corrode like the grounds but they can. It sounds like you're on track to clean up your electrics.

 

Update : Bought a new battery a week ago and Redram is back to normal so battery was the main issue. Cleaning all the grounds made the lights brighter and runs a bit smoother as well. Luckily didn't need an alternator.
Thanks to all that helped!

 

I don't know how many times I've worked on something that the owner over thought. Grounds have always been a slow problem developing. Batteries are the same way along with shock absorbers. They fail so slowly, when you fix it, it's a drastic improvement.