This has not much to do with MG, until you consider "upgrading" rear suspension to modern technology. A prerequisite for this course is RS-106 for understanding of elliptical leaf springs.

Circle, ellipse, parabola, and hyperbola are all conic sections that can be expressed using the same quadratic equation. Parabolic springs are a very special configuration of a leaf spring. The "parabolic" spring takes the multi-leaf elliptical leaf spring one step farther and turns the spring of varying thickness into a single leaf. To have equal stress over the full length of the single leaf spring, it has to be thicker in the middle and thinner at the ends. When you do this the thicker section in the middle bends less, and the thinner section near the ends bends more. So to end up with the desired flat condition under load, the initial unloaded curve form needs to be a parabola rather than an ellipse. Therefore the name, parabolic spring.

As fate would have it, the newer technology composite springs (graphite or fiberglass) with single leaf may be parabolic as a simple exercise of good engineering design, along with being thick in the middle and thinner at the ends. (See article RS202).
With composite springs, lighter weight may be the primary objective, and loss of inter-leaf friction is a collateral bonus. For a leaf spring that is attached to the frame at both ends, and to the live axle in the center, slightly more than half of the spring weight will be un-sprung weight. Changing two springs from 40 pounds to 10 pounds reduces vehicle weight by 30 pounds, and un-sprung weight by almost 20 pounds.

That's all good in my book, but I'm not sure I want to pay for it. I suspect the parabolic or composite springs are not allowed in most racing classes, especially vintage racing. For street use it may be more a matter of feeling rich and wanting to spend some money to improve ride quality and handling a bit. I kind of like my vintage MG the way it is. If you reduce weight and improve acceleration and handling and ride quality, you might spoil the vintage car experience. How much money do you want to spend to drive a Mazda or Honda the looks like an MG? Anyone checked out the cost of an S2000 engine and chassis conversion recently?

On the other hand, if the special composite springs were same cost or cheaper than standard replacement springs, we might have something popular (like aftermarket electronic fuel pump).