Attractive non-local interactions jointly with repulsive local interaction in a microscopic modelling of electronic Fermi liquids generate a competition between an enhancement of the static charge susceptibility---ultimately signalling charge instability and phase separation---and its correlation induced suppression. We analyse this scenario through the investigation of the extended Hubbard model on a two-dimensional square lattice, using the spin rotation invariant slave-boson representation of Kotliar and Ruckenstein. The quasiparticle density of states, the renormalised effective mass and the Landau parameter \(F_0^s\) are presented, whereby the positivity of \(F_0^s-1\) constitutes a criterion for stability. Van Hove singularities in the density of states support possible charge instabilities. A (negative) next-nearest neighbour hopping parameter \(t'\) shifts their positions and produces a tendency towards charge instability even for low filling whereas the \(t'\)-controlled particle-hole asymmetry of the correlation driven effective mass is small. A region of instability on account of the attractive interaction \(V\) is identified, either at half filling in the absence of strong electronic correlations or, in the case of large on-site interaction \(U\), at densities far from half filling.