Well, my soldering iron has been working overtime since reading all your answers. I've done a bit of experimenting with caps, & I've tried .1, .047 & .022.
I was reading the descriptions of what different size caps do, & I couldn't really understand what was meant. When I heard that a .022 was brighter, I assumed it wouldn't suit me, as I don't like a Strat to sound too trebley, but .022 seems the best compromise for me. I guess it depends how you use the tone control - I tend to use it to roll off the top end to sort of fatten the sound up a bit. I know a passive tone circuit can't actually fatten up the sound as it doesn't add any mids, but taking off the top end only makes the mids more prominent.
With a .1 cap, it seemed to roll off too much of the high-mids as it was turned down, leaving me with a sound that was not only too muddy, but lower in volume too. It was this loss of volume when the tone was turned down below about 4 that I didn't like. .047 was better, but with a .022 cap I think I finally understood what is meant by Clapton's "woman tone". With the overdrive turned up a bit, I can turn the volume to 10 and the tone to 1, select the neck pickup (or the neck/middle) and get a really nice usable fat sound. Excellent sustain, thick and fat, but not too muddy, and without too much loss of volume.
I did wonder whether using a .022 would mean that I had to turn the tone control down further to get a usable sound, but it doesn't seem to work like that, which is good. So, I think I've now decided to use a .022 cap on any Strat or Tele that I own.
However, different guitars and different pickups seem to react differently to the caps that are used, which isn't really too surprising. My 88 Strat had the .1 cap, but it also has Texas Special pickups. When I first fitted them earlier this year, I loved them, but now I'm not sure that they're the improvement that I thought they were. Does anyone else have views on Texas Specials, particularly in comparison with standard vintage type pickups (such as Seymour Duncan Vintage or Alnico 2s?).
My old favourite 86 Strat has a ceramic .047 cap, and it sounds great, but I'll try it with a .022 and see if it's an improvement. I've ordered a Vitamin Q .022 from Allparts, so I should be able to fit it later this week.
I also found some interesting .022 caps from http://www.axesrus.com/
They're on this page:
http://www.axesrus.com/axeknobs.htm
and they're described as "Very old Vintage .02 mfd capacitors". I'm not sure what they're made of, but I get the impression they may have a slight edge over the Orange Drops, but it's early days really, time will tell. Has anyone else tried them?
So that's it for now, all I have to do is play the guitars and make sure I still like the .022s after I've used them for a while. Thanks to Tudor and everyone else who patiently explained this stuff to me, it was a big help. And I hope my experiences might be helpful to a few other people too.