I'm sure you've already considered this, but you can think about the individual components of your speakers, and then how those components work together.
For example, your existing speakers have a box or "cabinet." Is is sufficiently inert (well-braced, rigid, etc.)? If not, can you improve that? If you wish to keep the existing boxes, have you calculated their theoretical frequency parameters using one of the online calculators (you can input the electromechanical properties of different drivers and see how things change)? But doing things like changing drivers also likely means changing crossovers, and even the drivers' placement in the baffle may be compromised.
Cerwin Vega speakers are known for being "fun," but not particularly "accurate" or adept at reproducing subtleties. I think it's unlikely that you will be able to improve the overall performance to make them more audiophile-like in a cost-effective manor, with the possible exception of reducing cabinet flex and resonance. I'd enjoy them for what they are, and when you decide that you'd like different qualities you can go looking for a different set of speakers that has what you are looking for.