Cracks in the swingarm are usually caused by the overloading of the suspension, whether it is the shock pre-load, combined rider and passenger weight or pulling an overloaded trailer or too much tongue weight.
Basically, it has reached it's limits of abuse !!:Shrug:
The cracks should be addressed first and repaired depending on the location and then re-enforced.
Look at another thing that affects the ride height, rear swingarm isolator bushings.
These bushings are used to attach the swingarm to the rear axle and they are made of polyurethane.
Polyurethane has a definite shelf life and I suspect that the original bunch of bushings were all made at the same time, about 14 years ago.
When they fail, the rear end will drop down an inch or so and the driveshaft will start rubbing inside the swingarm (making noise).
Check all of those items before you get the Progressive 1100-1200 Spring.
Measure your OEM spring first (with a micrometer) to see if it had not already been replaced.
Stock OEM spring is .500" and the 1000 - 1200 is .535"
I also have a Heavy-Duty auxiliary shock and spring to replace the standard lateral auxiliary shock.
Hope this helps.