I'm doing some technical work, where I'm measuring along lines in a bitmap. To help in the measurements, I:
place guides all over the place, then
trace the line of interest with the bezier tool, clicking to put nodes at each intersection with the guides, then
use the node tool to cut the path at all the (internal) nodes, then
select the selection tool, and break apart the path into separate segments, then
I measure the length using the Extension: Visualise Path > Measure Path...

Is there some way I can make this go more quickly?

The only thing I can think of that might be faster, is to skip the step of placing Guides. Could you just use the Pen/Bezier tool and trace over the lines, without using Guides?

It is possible to convert objects to guides, but not vice versa, unfortunately.

Or since it's a raster image, why not use a raster graphics program? I know that The GIMP has a measuring tool. It's another open source project, a bit more mature than Inkscape though. But still free.