All springs are designed for x number of cycles, usually 1 million. This assumes they are not loaded beyond the elastic limit. Above the yield point they will set and not return to the original shape. A torsion bar will not normally crack unless struck, notched or other discontinuity because it the range of motion is more limited than a typical leaf set up, and it doesn't have the stress risers than can exist on coils (near the ends). The rate on a million cycled t-bar is the very close to new. If the front is sitting a little lower, just turn the adjuster in.
That said, most people who like a sporty car will prefer a larger t-bar than factory offerings. It will reduce body roll and that will keep a better contact patch when cornering. The other approach is to use a larger front sway bar, or do both. Either of these increases the load on the outer tire during cornering, so the improvements felt are eventually limited by the outer tire getting overloaded.
Formula S cars came with better rear leafs than the rest of the a-body line. Unfortunately, leafs springs are all too easily pushed past their yield point due to shape and design. If the car hasn't been towing stuff, used to carry bags of cement, or run at the dragstrip, the leafs could be worth rebuilding. Interleafs, clamps, pin, bushings are nothing special, go ahead and replace those. It's the main leaf and to some degree the second leaf that are most critical to making the Forumula S (& later also the 383 equiped a-bodies) rear leaf packs better.
Formula S shocks were advertised as being different, IIRC 'heavy duty' was the term. But I haven't check the part books to see if they were different p/n than came on a 'heavy duty' optioned car. (even then, I'm sure concurs restoration people would have more info for what was actually used in the assembly line)
