Okay here we go...
1. 'Orange Drop' means nothing. There's multiple "orange drops" including Sprague 6PS and Sprague 715P both 'orange drops' both VERY different composition 6PS is polyester, 715P is polypropylene... whatever you heard about them is likely snake oil. One thing I CAN say, is that Polypropylene will be more stable than Polyester, ceramic, and paper in oil. That would be the only 'upgrade.' the value is what determines tone, in this application. If we we're talking about active circuits in amps, it's a different story. Passive tone controls, only the value matters.
2. A 47nF cap wont really 'smooth out' the tone pot response, in fact, I'd argue it'd do the opposite. 47nF will cut off highs quicker and more sharply as you roll the tone control back compared to a 22nF. To me, that makes the roll off more sudden and abrupt..
3. You can absolultely switch to whatever caps you desire, here's a list of values I have in different guitars. 2.2nF, 2.7nF, 3.3nF, 6.8nF, 15nF, 33nF
All for different purposes. As you decrease the cap value, the highs are cut less sharply, and when you roll the control to '0' it creates a new resonant peak. In the case of the very small values like 2.2nF, I use it to shift the resonant frequency lower, to mimic a warmer sounding pickup like a P-90 or humbucker. As you increase cap value, you cut more highs, at an earlier frequency. So, IMO, the only reason to go to a 47 would be if you're rolling the 22nF back ALL the way, and somehow, it's not cutting enough highs. I usually dont find this to be the case, with a few exceptions. For example, my E-Bow adds a ton of overtones, the extra high cut, is a bit more useful in that situation. Personally, I find 22nF too large for many guitars. You wont hurt anything experimenting, unless you're clumsy with the soldering iron
4. The 22nF for humbuckers, 47nF for single coils, 'rule' is bullspit, IMO. Yes, those are values typically used for them, but there's zero reason you need to, or should follow that. The tone circuit will interact with your pickups inductance and capacitance. This will vary throughout single coils and humbuckers. P-90s are single coils with inductances very close to humbuckers (6-8Henrys) Single coils can vary greatly, as well as humbuckers. Generally, the greater the pickup inductance, the more highs that will get cut, for a given tone cap value. This is why you'd generally use a lower value cap for high inductance pickups like humbuckers. Still, there's no steadfast rule and it's greatly up to the player's tastes. In many cases I find the standard 22nf and 47nF values too large for the tone control to be fully effective. I find it mushes and muds up too, quicky, and I find that most of the tone control's range is pretty useless. That's why I generally stick to smaller value caps.
Also, some people make the mistake of assuming a 47nF rolled back partially will be like a 22nF rolled back a bit farther. Because of this many people seem to think the 47nF is more versatile because it seemingly has a bigger range. And while, yes, you do get more cut with the 47nF, the frequency, and sharpness of the cutoff will be different between the two caps. The bigger cap will cut more midrange frequencies, than a smaller cap, which will result in different tones
Here's the good news. Unless, you're getting ripped off, caps are usually not much more than $1, if you even pay that much (composition will effect price-Ceramics are cheapest, and why they're installed in factory mass produced guitars)
Buy a bunch of values, and try them, see what you like best. They're really easy to swap too, so experimenting is real easy.
If you want a smoother tone pot response, I'd recommend a 10nF, personally. It'll still give plenty of high end cut, but wont muddy up as quickly as larger caps.
My ASAT Deluxe has a 6.8nF (recently lowered from a 10nF-original value=22nF), my Legacy has a 2.2nF(lowered from 22nF), my Superhawk has a 3.3nF(22nF originally) and my S-500 has a 15nF (will be swapping to a 8.2nF, in the near future.. Original value was 22nF, IIRC)
Hope that helps. Dont buy any $10 caps.