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Dan Weisz (@bigticketdw) and I wrote a white paper on Near-field Cosmology for the Astro2020 decadal survey. The main point: the study of nearby galaxies on a star-by-star basis has big implications that extend far beyond the nearby Universe. arxiv.org/abs/1901.07571
For example: SED-based interpretation of faint, distant galaxies relies on calibrations within the Local Group; nearby, low-mass galaxies are currently our only probe of the matter power spectrum on small scales and can tell us about the reionization era.
A key tool for this field is resolved color-magnitude diagrams because they allow us to reconstruct a galaxy's star formation rate over time. This is especially useful for nearby faint galaxies, as their progenitors were even lower luminosity & are probably invisible to us today.
It is crucial that these CMDs extend to the oldest main sequence turn-off; anything less does not give sufficient time resolution when reconstructing a galaxy's star formation history, particularly at early times. 
Right now, resolved CMD studies are limited to the Local Group (and mostly to the Milky Way). JWST will push out farther, but its limited sensitivity at blue wavelengths makes it challenging to go further. Much larger space-based optical/UV observatories would be transformative.
Dissecting galaxies in the near field will allow us to better understand faint galaxies at all times; this is especially interesting in the reionization era, as we can make inferences about populations that *must* exist but will likely never be seen directly.
These same galaxies in the near field also can tell us about properties of dark matter, both in terms of the initial spectrum of fluctuations and interactions in the deeply non-linear regime.
Finally, we censored ourselves and did not title the paper "I've got 99 references but Eggen, Lynden-Bell, & Sandage ain't one". With hindsight of ~12 hours, it's pretty clear this was a mistake. arxiv.org/abs/1901.07571
