I have 4 possible upgrades in mind. I believe the first three are roughly the same cost:
Upgrade from Bartok to Rossini (the only thing truly relevant to this group);
Upgrade (speakers) from Borresen 01 to Borresen 01 Silver Edition;
Upgrade (speaker cable) from Ansuz C (version 1) to Ansuz D2;
Upgrade (server) Melco N1Z/2EX-60H to new (single drive 4 TB) N1Z/2EX-40S.
The last is ~ 60% of the cost of the first 3.
In the real world I cannot possibly listen to each of these in my home system (and room). Any words of wisdom, if any, are greatly appreciated, as always.