The HE speakers' drivers have silver coils rather than copper, so while you give up some of the volume of strands from SPx to SPe, you simultaneously replace significant copper components with silver ones. The HE series of speakers, all else being equal, resolve low level detail better than their non-HE counterparts, which, as you know, are scarcely slouches to begin with.
I would say that going from SPx to Lexus rather than SPe in the HE form would give you a more 'muscular' sound, and one that would be more forgiving of upstream components, but since you're using Fi amps, I wouldn't expect the latter to be an issue. I think you would give up some of the refinement you're accustomed to with the SPx. It's difficult to judge for someone else, but I think that might be going to far for the sake of economy.
Another significant point is that I assume your E/Spx have the traditional paper cone, not the hemp cone now being used. The ability to resolve still finer low-level detail, which was already strengthened by the transition to HE, leaps further ahead with the hemp cone. The difference is not subtle!
In the next month I'll be getting back a pair of Lexus Signatures which were built with paper cones and, after re-familiarizing myself with the fine points of their sound again, I'll be changing out the woofers for the hemp cones. I'll report what I hear on my blog, linked below.
Keep your ears and your mind open.