Nuttymut, sell your silo's 3 at a time (whenever you have enough gems for improved silo) for granite and you will have your level 5 costs for improved silo right back from the trade office.
Silo's might be obsolete to you as a paying player lvl 50 in need of buildingspace, but for lvl 40 player non paying the building might still have value in reducing Island maintenance at the point where there are going to be ever more farmfields collapsing daily.
Just like the houses may become obsolete with the introduction of frozen manors, they also still have market value.
Exo wood isn't all that expensive (on TradeOffice) and hardly worth mentioning here.
OW btw gemprize of 3 silo vs 1 improved silo differs 5 or 10 gem?? (maintenance at the moment so can't check) so your idea that BB would introduce the improved one cuz of gemcost seems farfetched, unless you are telling me you buy exowood and granite with gems instead of adventuring, lootspotting and trading to get them???????
(I myself pay for gempits now and then, but i will never spend even 1 gem on resources i can get for free from gameplay)
Bluesavanah that's maybe why grout is invented and level 6 instead off creating an improved farm.