A dirty flash is just installing a new Rom without wiping anything first. Depends on what you are flashing whether a dirty flash is OK. Usually if you are going from one CM nightly to another say CM 10.2 from yesterday to CM 10.2 from today you can get away without wiping caches. If on the other hand you want to go from CM 10.2 to Cm 11 you really should wipe caches first, same going from say CM to Carbon it is recommended to wipe first.
There are a few kernels out there but they are specific to certain Roms. There were some touch kernels for CM 10.2 but they only work on early releases not the stable. Unless you have a specific need I would't worry about flashing a new kernel.
More importantly, does wiping datamedia influence anything (configuration wise) that latches to rom or kernel? I mean, is there any information stored in the files that are wiped by "wipe datamedia" that is used by the kernel or the rom?
I'm asking this because I currently have the audio out jack kinda broken since I've tried some kk roms (delivers very bad quality audio, whereas the speaker has good quality) and I don't know what else to do. I've tried to change from kk to jb without datamedia wiping, but this didnt solve the problem, so I'm asking to know if maybe the kernel stored some bad audio quality config file there (in datamedia) and a wipe there could solve the problem.