I am thinking about changing the lower control arms to tubulars when I have my disc brake conversion done. I am rebuilding the front end with the brakes, new shocks and springs. Also replacing the bushings with a performance suspension super front end kit. The car is having a 400 SB dropped in as we speak. Is it worth the extra 5-600 dollars to add this upgrade?

I have a 69 convertible

They won't provide any steering geometry changest whatsoever only the uppers that are out now will provide that. The advantages are strength(you can also strengthen your stock arms) and of course the looks. There are a few different options out there as far as lowers but if you are looking for some sort of handling advantage your are barking up the wrong tree.