Well, let me hit on one thing that I am very vocal about, I don't care what caliber you are shooting, ALWAYS, ALWAYS wear hearing protection. If need be, buy a pair of muffs that only cancel out the noise over a certain Db level. They are not expensive (75-125 fo good ones) and are much much less than you will spend in battries alone for five years for your hearing aid later in life.
Okay, on to the good stuff.
The .22KH is a pretty significant improvement over the standard Hornet in terms of both speed and accuracy. No don't get me wrong as there are a lot of Hornets out there that will out shoot 99.5% of shooters, but overall, all the KH's I've seen shoot more accuratly with less trial and error than the standard version. The loss of case life is generaly due to FL re-sizing rather than neck only sizing but there are many hornets out there that just plain shoot better when the cases have been FL sized. They are less noisy than the .223, but you can certainly down load the .223 to match the same general performance you'll get from the .22H or .22KH though you may give up a bit of accuracy, (may; not will).
As far as I'm concerned I'd buy the extra barrel it will only cause you to have more fun experimenting with a new caliber.