inferno will not yield any more exp that hell will. the spawned mobs do not give exp themselves. and the kill streak bonus applies the same in ALL difficulties
also my results only netted about 4-5k XP per minute from the kill streak, 838 mobs over 35 minutes, kill streak was 171,000 XP = 4800 XP per minute
even with XP gear you will only gain about 7k XP per minute
the towers spawn 3 mobs 5 times per minute, 2 towers will give you 30 mobs per minute, and assuming your getting 250 XP from gear per kill = 7000 XP per minute
at best with an XP gem your looking at 15k per minute or about a million XP per hour
overall its just not worth it other than the fact that it is AFK