  In the recent literature on dark energy (DE) model building we have learnt
that cosmologies with variable cosmological parameters can mimic more
traditional DE pictures exclusively based on scalar fields (e.g. quintessence
and phantom). In a previous work we have illustrated this situation within the
context of a renormalization group running cosmological term, Lambda. Here we
analyze the possibility that both the cosmological term and the gravitational
coupling, G, are running parameters within a more general framework (a variant
of the so-called ``LXCDM models'') in which the DE fluid can be a mixture of a
running Lambda and another dynamical entity X (the ``cosmon'') which may behave
quintessence-like or phantom-like. We compute the effective EOS parameter, w,
of this composite fluid and show that the LXCDM can mimic to a large extent the
standard LCDM model while retaining features hinting at its potential composite
nature (such as the smooth crossing of the cosmological constant boundary
w=-1). We further argue that the LXCDM models can cure the cosmological
coincidence problem. All in all we suggest that future experimental studies on
precision cosmology should take seriously the possibility that the DE fluid can
be a composite medium whose dynamical features are partially caused and
renormalized by the quantum running of the cosmological parameters.
