What exactly does "efficiency" mean? Does it reduce time spent per action, or motivation spent per tick? Or both?
It's both.
Let me paste the equations I didn't post them on itch yet.
The efficiency bonuses from stats multiply the costs by 1 / (1 + StatLevel / 50)
The XP bonus from permanent levels multiplies XP gain by 1 + ((Level ^ 0.8) / 5)
Most skills multiply costs by 1 / (1 + SkillLevel / 25)
MNST, FISH, and BIRD multiply the cost of removing rocks by 1 / (1 + Level*ResourceAmount / 100)
The STAT skill adds a flat 4% of your permanent level to your current level for each STAT level.
By default you get 100 skill XP per learn. The XP cost starts at 30-90 and goes up by the original cost every level. LERN gives 4 extra points per level.
Yeah that's fair. If you don't find the power growth in it satisfying then you won't be the only one.
I don't know if it will help at all but I can explain more about what is going on at least. MTVN is spent at a constant rate so reducing costs does make it go faster. For the stats the permanent level is just a XP bonus for the daily level until you get the STAT skill, and at first the loops are short so the daily level won't go very high and it won't be very noticable, but when you get access to more flowers and can have longer days then you can see those stats build up and your speed increase more over the day.
That was the idea anyway. If I make something else it will be easier to understand and feel progress.