I've just switched off the C30 after testing the mods I did and... wow! it does work! 
Now it got a REALLY good sound on the clean channel, very Fendery.
It has a Twin-like frequency response, with slightly scooped mid, sparkly at the right point with a lot of "dong" on the bass side.
Ok, it's not a Vibrolux, but for the money and the work I did it has more or less the type of sound I was lookin for.

Here are the things I did:

* took out C10 and R10 
* changed R6 with jumper
* changed C8 with a 33K resistor and R10 with a 1M Resistor
* changed R1 with a 100K resistor
* changed the slope resistor R19 with a 100K R
* changed C18 with a 100nF 
* changed C19 with a polystirol cap, same value
* put a 330K R across the 1M bass pot
* put a 15K R acorss the 20K Mid pot 
* changed C11 with a 1nF cap
* changed R12 with a 1.8M resistor
* changed R7 with 470K
* lit up a cig after the work

the boost now pumps the mids a little and it's, at least, usable.
I made a mistake, I've done all the things together, so I don't know exactly, for example, how R7 changes the tone.
But I'm really happy with it so, as soon as possible, I'll record something and I'll put it on my site, to let you hear the amp.
I'd like to thank you all for the help, especially Steve and Chris.
bye everybody,

Marcello