I own SongTowers with the dome tweeter (my impressions and photos are linked in my signature line below), and am very familiar with Vandersteens. My brother owns a Vandersteen 5.2 system – 3As with two V2Q subwoofers, but I don't remember the center and rear speaker models. When he shopped I tagged along for fun, and we listened to the 2s for some time until he decided on the 3s.
I like the Vandys a lot, they're among the best imaging speakers I’ve known. On the downside they are at best strange looking (but you've been happy with yours for quite some time) and they are very finicky about speaker and listener position. Their sweet spot is small, but once you’ve found it, it's wonderful. Until I got the STs, the Vandy 3A was my favorite speaker.
The Salk SongTower, with either the standard ¾" dome or the ribbon tweeter, are truly excellent speakers. They are tonally well balanced, with a nearly flat frequency response, and unlike the Vandys, they have very wide sound dispersion. Their sweet spots are very wide and their imaging is excellent. I think that the ST would be a worthy replacement for your Vandys. Your room size and amp will be fine with the STs. Keep your sub, its excellent. The sound of the transmission line bass of the STs will surprise you. They also allow great flexibility in room placement for bass sound. Few, if any, people have had difficulty blending STs with their subs.
I've also heard the recently released Philharmonic Audio speakers. The Philharmonic 2, as you probably know, is the same price as the standard ST. To me, they are very close in overall sound. The Phil has deeper bass, but is a bit less sensitive. It's a 3-way speaker with black (at that price) 2-piece cabinets that need some space, especially from side walls. Your big room should not be a problem for that. People talk on and on about the RAAL ribbon tweeter, but I think the real outstanding feature of the Phils is the planar midrange. It creates a clean and detailed sound. Varying the amount of stuffing in the semi-open back cabinets allows you to vary the balance between the front wave and rear wave coming from these drivers. At Dennis Murphy's house and last July at the Capital Audiofest, I heard how this can let you change the soundstage depth, and also vary the relative front/back placement of voices or instruments. Except for the Salk SoundScapes and the DIY Statement speakers, this feature is unique.
I'm not clear if your price range is for all 5 speakers, or the front pair. If it is for the just front pair, you should also consider the Salk HT2-TL. Its more than double the price of the standard ST, but it is worth it in my opinion.
I've heard several Joseph Audio models, including the RM25XL, at audio shows. I like them, but their prices, in my opinion, are too high. The RM25XL costs, if I remember correctly, about $4000 per pair, and it sounds roughly comparable to the Salk SongTower. At that price, I'd much rather choose the Salk HT2-TL. I think the Joseph Audio Perspective is comparable in overall sound with the Salk HT2-TL, but costs much much more.