maintaining 50% RH would keep the dew point sufficiently low to mitigate mold under rugs, (the dew point of 70F 50% RH air is about 50F) but in basements with lots of air leakage that can add 100s of kwh to the annual bill.
I use about 150 kwh for dehumidification for the entire year, so I might be able to save $10 by going higher. But 50% is a good level for keeping rust off of tools (and is pretty optimal for people), so I'd keep it there no matter what I had on the floor.
If I had concerns about dehumidification costs, I'd use a timer and dehumidify to 50% for only 4 hours every afternoon. This would be even less expensive than a constant but higher %RH. Evidently this technique is effective for mold prevention in unoccupied Florida homes (use of A/C while unoccupied is wasteful).