Re: String change on RG (.009s vs .010s)
I wouldn't say thicker strings equal better tone. It's not better, it's different, and whether or not you prefer it is entirely subjective.
My experience has been that thicker strings have a more compressed attack than thinner strings. This makes them sound a bit darker and less "snappy" than lighter strings, comparatively, and the smoother attack coupled with the slight increase in volume due to the added vibrational mass (think of it as like inertia, basically - tougher to get into motion, but they'll stay in motion better) does give you a little bit of boost in sustain, both actual (due to the mass) and percieved (due to the attack jumping out less).
Now, whether or not this is good depends on a number of factors. If you play a bright, naturally uncompressed rig with an already bright guitar, then unless you like the brightness and lack of compression, you'll probably find the tone "better." SRV is the perfect example - a stratocaster into a fender amp will produce a LOT of high end and sharp attack unless you do something to take the edge off a little, and the heavier strings smooth out his jackhammer-like attack a bit, giving the impression of more "body" to the sound. On a dark guitar driving a dark rig, you probably want all the attack you can get, and adding heavier strings will probably just make you sound "muddier" than you would with light strings. Satriani is actually a pretty good example here, especially early in his career - his live tone from his Marshalls and DS-1 was pretty dark and smooth, and 9's allow him to still get a powerful attack through that setup.
FWIW, I play a Universe strung up with 11-68's into a Mesa Nomad. I'm of the bright guitar/dark amp school of tone, so you'd think I'd want to go with 9's with this rig. I did for the longest time, too, but I seem to phrase better on heavier strings - my bending sounds better to me when I have to fight a bit, someohow - and honestly, the tonal change isn't THAT big, so I just screwed with my EQ a little and I'm still getting a tone I'm really happy with.