I've been using the line through Market Harborough fairly regularly for the past ten years, occasionally for the ten before that. Will the time saving affect my propensity to use the line ? Probably not.
It is an improvement, but in terms of getting people on public transport, the real improvements on the main line come if you have one that's at or close to capacity, and you get to release an additional path or two. Of course you'd usually need a few Market Harborough type projects to release a path.
You, yet again, fail to see the bigger picture - quicker times on a mainline means the intercity trains can improve their times over any particular junctions and clear them quicker, or, maybe be routed into easier platforms in cities on its routes - thus it creates extra time and space for better journeys for the local services that may need them.
So 30 seconds quicker into Sheffield could reap far bigger rewards to far more people than a line opening to Ripon