To answer the original question, I think we shouldn't confuse the issue by discussing speakers that don't have the LCY ribbon tweets. For Salk, the SongTower RT, HT2, and V3 all have that same LCY ribbon. The HT1, HT3, and QW have the G2 tweeter. While they are very good speakers, the G2 tweeter is quite different from the LCY and they may have different dispersion qualities that may significantly affect imaging.
I own a pair of SongTowers with the standard Hiquphon OW2 dome tweeters, and I have heard a single version of the SongTower with the LCY ribbon. It was the prototype that Dennis Murphy used while designing the crossover with the LCY tweeter. Because it was only one speaker and not a pair, I can't compare the imaging of these two speakers. But I can compare the other sound qualities of these two speakers that were apparent while listening to single copies of each.
I thought the ribbon tweeter SongTower sounded somewhat cleaner or less noisy than the dome tweeter SongTower. I only heard this on quieter music that featured a single singer or unamplified musical instrument like a piano. Louder music masked this difference. Overall this difference was, in my opinion, subtle. I am 59 years old and have ears typical of men of that age. Your high frequency hearing may differ.
Now about imaging. First of all, much of the excellent imaging of the SongTower comes from the fact that the 5½" SEAS midwoofer is crossed over to the tweeter at about 2500 Hz. This crossover frequency is similar (if not identical?) for both versions of the SongTower. At this range, the midwoofer's off-axis dispersion is excellent. The response measured 60° off-axis at 2000 to 2500 Hz is less than 3 dB lower than the on-axis response. This is much better than most other speakers I have known.
If a primary tone is somewhere in the midrange, say about 500 Hz, the 1st harmonic overtone is double that at 1000 Hz, and the second is at 2000 Hz. All these are in the range of the midwoofer, not the tweeter. For that primary tone at 500 Hz, the tweeter only starts contributing with the 3rd order harmonic at 4000 Hz. The OW2 dome tweeter begins to get narrower dispersion only above 10 kHz. In this range, we are only hearing harmonic overtones well above the primary music tones. For the LCY ribbon tweet, I'm not sure at what frequency range it begins to loose off axis performance. I do know that it is said to perform better at this than most other ribbon tweeters (hence my comment above about limiting this discussion to speakers with the same ribbon tweeter).
So my main point is that while the dispersion of a tweeter is important, the dispersion of the midwoofer is more important for good imaging. I think that both versions of the SongTower will image very well because that is how Dennis intended the midwoofers to behave below the crossover point.
The choice between the OW2 dome or the LCY ribbon tweeter is yours to make. I think you should base that on your preferences between very clean (for the OW2) or ultraclean (LCY) sounding tweeters, and their respective prices. I would worry less about differences in imaging, and I would ignore any previous experiences with poor dispersion of other ribbon tweeters.
