Parameters for Stretch

Once I have (with stretch increase decrease) roughly attained a convenient layout I adjust using system breaks

Since you prepare sheets for choir there is now a split measure possibility which eases to have system breaks at lyrics breaks. Choristers, at least the ones who doesn't read notes at first glance, are usually fond of such a layout.

Thanks for the comments!

There is no single parameter that works as you describe, but the stretch commands work on a selection, so you could simply pick and choose where to apply it.

What I generally do, though, is apply it generously, then go back through and apply line breaks manually (click barline, press Enter) in places where I think I don't need quite so many measures on a system. In fact, for me, a score isn't complete until I've locked in all my line breaks like that - adding them even on lines where I am perfectly happy with the default number of measures. Which is why I added an option in Edit / Tools / Add/Remove Line Breaks to "lock" the current breaks by adding explicit breaks automatically.

Also, BTW, there is a standard of sorts called Modified Stave Notation put forth by RNIB (a British organization for the blind & visually imparied) that makes recommendations for various settings (staff line thickness, stem thickness, etc) for large print scores for the visually impaired. I guess the idea is, simply scaling up a normal score isn't ideal, but instead, some things should be adjusted. MuseScore actively supports MSN and provides options to create MSN through the settings available in Style / General. You might want to check out these links and see if there are improvements you could make to your template:

http://www.rnib.org.uk/information-everyday-living-home-and-leisure-mus…

http://musescore.org/en/tutorials/modified-stave-notation