I don't use Rose Hill so I can't comment on passenger numbers there, but as a frequent user of Marple station, and of its car parks, my impression is that parking (which has been very difficult for some years) may have become a bit easier in the past year or two. So maybe some people who used to drive a mile or so from the west end of Marple are now walking to Rose Hill instead? But that's a very subjective impression and I'm not too sure.
As for this:
I think it will help the local economy of Marple if travel to manchester is dearer.
...... I can't make any sense of it! People travel to Manchester for work, for entertainment (theatre, clubbing, concerts), and to shop for clothes and other special purchases, of which Manchester offers a range that certainly can't be met in Marple. So no-one is going to say 'I can't afford to go in to Manchester for work, or a concert, or whatever, so I'll get a job, or go to a concert, in Marple instead!'