These are all incremental improvements that should be relatively noncontroversial -- assuming we don't go the route of just rewriting the entire thing from scratch. If you are a committer, feel free to edit the list below to either add items or mark them as done.

• http://matplotlib.org/devdocs/examples/api/histogram_path_demo.html: Came in in cd88e29, technique seems quite low-level, corresponding animation example was removed three years ago in remove old animtion examples. #2779.
• http://matplotlib.org/examples/lines_bars_and_markers/fill_demo.html
  http://matplotlib.org/examples/lines_bars_and_markers/fill_demo_features.html slightly misleading, xref fill_demo and fill_between_demo are slightly misleading #5827. Done in merge fill_demo and fill_demo_features #8154, but still misleading IMO.

• http://matplotlib.org/examples/api/sankey_demo_old.html: remove (we have builtin support for such diagrams now). Done in MAINT cleaning up of gallery examples. #7972.
• http://matplotlib.org/examples/images_contours_and_fields/streamplot_demo_features.html http://matplotlib.org/examples/images_contours_and_fields/streamplot_demo_masking.html http://matplotlib.org/examples/images_contours_and_fields/streamplot_demo_start_points.html: should be merged in a single example. Merged streamline examples #8336
• http://matplotlib.org/examples/pylab_examples/equal_aspect_ratio.html: relies on plt.axes() to return the already existing implicit axes, which is not really documented directly; should use plt.gca() instead (given that it's a pylab example).
• Update vlines example with axes wide lines. #7878 modified examples/pylab_examples/vline_hline_demo.py to use blended_transform_factory, but that's really overkill: see Update vlines example with axes wide lines. #7878 (comment).
• http://matplotlib.org/examples/pylab_examples/newscalarformatter_demo.html: drop OldScalarFormatter (which should probably be deprecated anyways...) and use one formatter per subplot.
• http://matplotlib.org/examples/misc/sample_data_demo.html: remove, users should probably not rely on sample data. Done in MAINT cleaning up of gallery examples. #7972.
• http://matplotlib.org/examples/pylab_examples/spectrum_demo.html: add tight_layout() call. Done in Fix layout of spectrum_demo.py #8158.
• http://matplotlib.org/examples/pylab_examples/accented_text.html http://matplotlib.org/examples/text_labels_and_annotations/unicode_demo.html: remove Clean up and move accented text example #8065
• http://matplotlib.org/examples/pylab_examples/matshow.html: only keep middle plot Done in Remove example of matrix of size (12, 12) and (64, 64) #8094
• http://matplotlib.org/examples/pylab_examples/manual_axis.html: remove (deprecated) Done in MAINT cleaning up of gallery examples. #7972.
• http://matplotlib.org/examples/pylab_examples/text_handles.html: remove; it refers to an apparently non-existing text_themes examples which may be worth restoring (perhaps) Done in MAINT cleaning up of gallery examples. #7972.
• http://matplotlib.org/examples/pylab_examples/toggle_images.html: remove or move to event handling section. Done in MAINT cleaning up of gallery examples. #7972.
• http://matplotlib.org/examples/lines_bars_and_markers/fill_demo_features.html http://matplotlib.org/examples/lines_bars_and_markers/fill_demo.html: merge. Done in merge fill_demo and fill_demo_features #8154.
• http://matplotlib.org/examples/pylab_examples/tex_demo.html http://matplotlib.org/examples/pylab_examples/tex_unicode_demo.html: merge. Done in merged the tex_X.py files into a single file tex.py #8199.

attn @NelleV