While not in the class of SongTowers, I did migrate my 4 surrounds from KEF Eggs to Aperion Verus Grand Towers.
Frankly, I have to admit I rarely notice a difference. Even in big Bing/Bang/Boom movies, cranked up loud, the fronts and subs are so much louder than the surrounds I'm not sure I can really hear a difference. Fuzz is right about "good surround content", but I find that is much less common than I thought.
The only time it really makes a difference is in All Channel Stereo, when played loud. Since that is probably the least used mode of everything available on my AVR, it doesn't really matter so much to me.
That being said, I still have the towers for surrounds. But if I were starting from zero today, I probably would not.