I posed the question earlier: if I have one sugar lump available, but I have already upgraded prisms once, meaning that the next upgrade will require two lumps, should I wait for the next one to appear, or use the one that's available to upgrade something else now?
A bit of analysis seems to confirm what I suspected to be the case; the increased production from the upgrade should be proportional to the number of lumps it costs. The algebra is pretty simple.
For every building, figure out the production boost from the next level upgrade. As far as I can tell, this is 1% of current production from all buildings of that type in each case. Divide this by the number of lumps required. The largest of these quantities identifies the best building to upgrade next. If you don't have enough lumps yet, the best strategy is to wait until you do.
For example: currently I have one lump available, my prisms are at level 1, everything else is at level zero. The prisms are producing 981 septillion CpS. The next best buildings, the Antimatter condensers, are producing 170 septillion, which is less than one sixth of the prism output. So even though I need 2 lumps for the next prism upgrade, the best idea is to wait till that second lump is available rather than upgrade the condensers now.
I'm sure there is a moral hidden in here somewhere - something about sugar rationing.