no, they won't, they're a ripoff.
Think of it this way, what do you need for combustion? air, fuel, spark.
Do those increase the amount of air, in any way? No. the system is the same before and after the spacer. there is no benefit. Any "spin" on the air would disappate as soon as it hit the plenum.
Now a plenum spacer would increase the volume of air in the plenum, -which WOULD give you more power.
Woe to him who builds his palace by unrighteousness,his upper rooms by injustice,making his countrymen work for nothing...Does it make you a king to have more and more cedar?Did not your father have food and drink?He did what was right and just,so all went well with him. He defended the cause of the poor and needy,and so all went well...But your eyes and your heart are set only on dishonest gain,on shedding innocent blood and on oppression and extortion. Jer 22:13, 15-17