HTP's main advantage in the context of the air-refuelled spaceplane is that it's a room-termperature liquid so the tanker and it's hardware can be relatively standard, rather than trying to get into the unknown territory of air-refuelling cryogenics or pressurised gas. Basically, you'd "just" have to pay attention to the seals and materials used to handle the HTP. The Royal Navy were planning to use it for carrier-based SR.177s and at least one of the carriers got as far as having the HTP tankage installed, so moisture can't be that much of a problem with it.
Passing HTP over a platinum catalyst gets you 500 deg C, oxygen-rich steam, which makes a nice low-power rocket in it's own right: the Germans used this technique for RATO units in WWII. I presume I'm right in thinking that if you spray vaporised kerosene into that mixture then it will spontaneously ignite? If so, then that's another advantage, i.e. it doesn't need an ignition system, or have I got the wrong end of the stick? If I'm right, then it would have the advantage of hypergolics (reliable ignition) without the disadvantage of a huge explosion if the fuels became accidentally mixed (say in a crash).