Quantum effects are expected to disappear in the short-wavelength, semiclassical limit. As a matter of fact, recent investigations of transport through quantum chaotic systems have demonstrated the exponential suppression of the weak localization corrections to the conductance and of the Fano factor for shot noise when the Ehrenfest time tau(E) exceeds the electronic dwell time tau(D). On the other hand, conductance fluctuations, an effect of quantum coherence, retain their universal value in the limit tau(E)/tau(D) -> infinity, when the system is ideally coupled to external leads. Motivated by this intriguing result we investigate conductance fluctuations through quantum chaotic cavities coupled to external leads via (tunnel) barriers of arbitrary transparency Gamma. Using the trajectory-based semiclassical theory of transport, we find that the linear tau(E) dependence of the conductance variance shows a nonmonotonous, sinusoidal behavior as a function of Gamma. Most notably, we find an increase of the conductance fluctuations with tau(E), above their universal value, for Gamma less than or similar to 0.5. These results, confirmed by numerical simulations, show that, contrary to common wisdom, effects of quantum coherence may increase in the semiclassical limit, under special circumstances.