uniformity of staves without having to use spacers
I have been painstakingly putting in spacers to try to get all staves and pages to be uniformly in line with each other. Is there a better,easier way to do this; maybe from the beginning. I have also found that if I have to use a large number of extra instruments in, say, a Classical Orchestra, then some of the instruments go off the page and it is then a major task to get them back on page.
Comments
What you are asking for is 100% uniform spacing between staves. This was the default in version 2 and if you used it I would guess you always changed the default due to slurs running into text on the nearby staff (or something similar). In version 3, you could override default locations of items so staff spacing will be minimized, then figure out the largest space between two staves, but you will probably have the problem you mentioned about staves running off the bottom of the page.
Without seeing your score it isn't clear what is going on, but my best guess is what @mike320 is suggesting - you have markings above/below staves that would be creating collisions so MuseScore is adding space. If you move the elements to avoid the collisions, the space closes up autoamtically. If you prefer to allow the collisions, you can go to Format / Style and make the minimum vertical distance an appropriately large negative number (you are saying how much collision to allow). Then you can go in and resolve the collisions you care about.
If that doesn't help, please attach your score so we can understand and assist better.