what's the difference between a 34 inch bass scale and a 35 inch scale?

Answer 1

One inch.

Supposedly the 35" scale will give a more "solid" lower register with more definition and punch and a tighter "B" string on a 5- or 6-string bass.

You can read a (very) little about it here:

http://www.carvin.com/products/guitar.php?ItemNumber=XB75

Answer 2

The purpose of the extra long scale, (35in.) is to give support for a higher string tension, which yields a more defined tone on the B string of 5 and 6 stringed instruments or detuned 4 string basses.

Answer 3

1 inch !