If you're itchin' for an upgrade and love the Vandersteens then I would recommend moving up to the 2CEs or CE Signatures. The tweeter on the CE is much better and the overall presentation is more coherent. Given the market for used Vandersteens, it would probably only cost you a couple hundred $$ for the UG. Money well spent.
From there, I'd start experimenting with amps. Of those you mention, I'd recommend the ARC Classic 60, but given your room dimensions, that might not be enough. Perhaps an ARC D-115MK2 (of which the Classic 60 is a direct descendant) would be a better match. They can be found for about the same price as the Classic 60 and have almost double the power with ALL of the MAGIC.
Good luck.
From there, I'd start experimenting with amps. Of those you mention, I'd recommend the ARC Classic 60, but given your room dimensions, that might not be enough. Perhaps an ARC D-115MK2 (of which the Classic 60 is a direct descendant) would be a better match. They can be found for about the same price as the Classic 60 and have almost double the power with ALL of the MAGIC.
Good luck.