K&N filters are ment to have oil on them for the dust to stick to it, but the oil can go and stick to the MAF sensor, but if your filter is dry then maybe its OK.
As for the DV there are pages and pages on here of why its bad but in a nut shell, your ECU is pushed all its limits to cope with the fact its losing air some how, and in turn is prob over fueling about and messing with the lambda probes, your power is prob down because f it and longer use will mess your engine up, but its your car and up to you really it makes no odds to me.