Most improved last 10yrs: Speaker, amp, or pre?

Tube amplifiers with automatic tube biasing.

cartridges seem to have experienced the largest proportionate cost increases. I wouldn't say amps have improved much.

Not many categorical sonic improvements these days. The best sounded really good years ago as it does today. The categorical improvements are in areas of efficiency, cost, size, convenience, aesthetics, etc. but not sound quality.

What about loudspeakers materials?

Loudspeaker inclosure that use solid aluminum, composites, sandwiched woods and granite. Drivers made from ceramic, wood pulp, carbon fiber and diamonds.

You may have to back up and ask, "has there been any improvements in the last years?" :)