Sometimes you want to be able to select all text, or select all circles, etc. Inkscape offers only a roundabout way to do this: Edit > Find.

To figure out how to actually search for specific types of objects, use Edit > XML Editor. (or open the SVG in a text editor)

Hopefully these shortcuts help though:

text id="text"
rectangles id="rect"
objects with the same color see here
lines Inkscape doesn't distinguish between "lines" and "shapes". They are both considered "paths". I often use style="fill:none", but that will also pick up unfilled shapes too, if they exist.
dashed lines style="dasharray:" selects all lines,
and style="dasharray:none" selects UN-dashed lines,
so move the first to a temporary layer, and then move the second back to the original layer