As someone who has owned SP-100s for the past 11 years, I can sympathize with your situation. During the past few years, I have considered a wide variety of newer speakers as replacements for the Spendors, yet still have the SP-100s. Some that you may want to listen to are Daedalus Athena and Ulysses, DeVore O/96, Audio Note E series, and Tannoys. One thing that I have learned is that for someone who likes the Spendor sound there are very few alternatives that will satisfy. Another thing is that the SP-100 has so much potential that it deserves top-notch sources and amplifiers. From your description of your system, it appears you reached the same conclusion.
The practical alternative for me has been vintage speakers. At present I alternate between the Spendors and a pair of homemade speakers that use a vintage 15" Jensen woofer with Altec 32 horn and 802-8G compression driver. There is a photo on my system page. While not perfect by any means, the vintage speaker is actually more satisfying on most types of music than the SP-100s, and I say that as a Spendor fan. Just something to consider.