only affects cheap violins? first time I've heard that one - not syaing it's untrue, but it seems strange. I think it's more likely that a more expensive violin gets looked after - and if it's played regularly, the player is a little more sensitive to the sound since they want to get their money's worth.

I find it really strange that no-one has mentioned the sound post at all - this is a prime part of how the instrument sounds, and it need adjusting fairly frequently.

Also, no one seems to think that the bow makes a difference - or the age of the hair, or the resin and the residue of older resin.

There isn't really a way to prove sleepiness of a violin. The variables are not all able to be controlled sufficiently to do it reliably and repeatably: (some in the list below can obviously be kept the same - e.g. you use the same violin. But, some are introduce a lot of inconsistency.)

1. the player
2. the bow and its factors - resin, tension (yes, they get tightened before everytime you play, and how do you know you tightened it the same?), also centre of gravity does differ between bows, material (pernambuco, carbon fibre) and overall weight (though not by much - most violin bows weigh around 60g, and the variance is about +/-2g). A player needs to get used to a bow in the same way that they need to get used to an instrument.
3. strings - age of string, has the string been played in?, type of string - all metal through synthetic core, metal winding, through gut core, metal winding, through to all gut. the sound differs between even the same type of string - one synthetic core string will sound different to another (cf dominant strings to evah pirazzi).
4. the resin - not as much of a difference between resins, but plenty of room to con people also - heard about the resin with gold flecks in it? makes a hell of a difference to the sound... ;-)
5. the sound post - this is critical. this is not held to the body using glue - it's jammed in place. if this is not set correctly, it really affects the sound. you can get weird effects - e,g, strong lower tones and flat higher, and
6. The bridge - this tilts backwards over time, due to tuning, and additional tension during playing.
7. humidity - some players stick humidity 'worms' into their instruments to keep them at the correct humidity.
8. temperature - affects the strings and the player mostly!
9. fingerboard 'action' - players tastes differ a bit in the action of the instrument - some like a bit more space between the string and the fingerboard, though this is rare for classical musicians. the nut, bridge and fingerboard angle all affect this
10. violin design - fat depth (like French) or thin depth (like Italian). French sound rounder, won't go as loud; Italian sound thinner, goes much louder. Great violins break this rule - e.g. look at a Gagliano - some are loud enough for concerto with orchestra. Then how big is the bass bar? the f-hole's width (& general size)?
11. violin material - what sort of woo?
12. varnish - thickness, type, age, how much UV radiation it's had.
13. dust/dirt and crud that's worked inside the instrument over time

enough for now, this reply is getting abit long, and I should be looking at some Shostakovich... (this may be structured procrastination!)