Perhaps a good option would be to introduce and, more importantly, discontinue gear at a more frequent pace.

For instance, this seasons, top end Noble sets could be replaced with a Lord's set (which would be similar or even identical in stats, but have a different appearance). After a few weeks/months, follow up with another replacement set, maybe an Odin's set. This way, the economy keeps churning to keep up with the new introductions. Also, it would allow the older, discontinued sets to increase in value for collectors, like the Founder sets have.

Another possibility, along the same line of thinking, is to introduce top-end weapons, all with the same stats, but with different Procs. So, for instance, the Bonechill Bow of Potency, with it's additional damage proc, could be replaced by the Odin's Recurve of Doom, which has +5% Crit Proc.

I don't think that this would have any negative impact on the economy, nor on player inventories. Essentially, it would be similar to the Sealord vs Demonlord thing. The stats are identical between the two sets, and it is more a matter of appearance. You also get the added benefit of a diversity in appearance for your toons without having to sacrifice stats.

I think three top end set introductions per season would really help to stimulate the economy. STS could also really engage it's user base in the same way as the Design the Banner contest. I suppose that we can't design every element in game due to hardware/memory limitations, which is why STS reuses the same 3D mesh objects, but at least one user designed set per season would be fun.

Plus, this would give the hardcore farmers and collectors something to look forward to, and something to buy/sell/trade. There isn't much point to having 5 Noble Doublets of Will unless you know that it's value will increase as soon as it is discontinued - because the way it stands now, the pricing of these items are in free-fall, so you are losing money holding onto them.