  We develop a new approach to the isospectrality of the orbifolds constructed
by Vign\'eras. We give fine sufficient criteria for i-isospectrality in given
degree i and for representation equivalence. These allow us to produce very
small exotic examples of isospectral orbifolds: hyperbolic 3-orbifolds that are
i-isospectral for all i but not representation equivalent, hyperbolic
3-orbifolds that are 0-isospectral but not 1-isospectral, and others. Using the
same method, we also give sufficient criteria for rationality of regulator
quotients Reg_i(Y_1)^2/Reg_i(Y_2)^2 for Vign\'eras orbifolds Y_1, Y_2,
sometimes even when they are not isospectral. Moreover, we establish a link
between the primes that enter in these regulator quotients and at which torsion
homology of Y_1 and Y_2 can differ, and Galois representations.
