Does this mean that people that have a FP+ for MSEP, but not for wishes can stay there to watch wishes? Or did you mean those that have both?
It was reported by at least one poster who had FP+ for MSEP that the CM's there
said that he/she/they could stay in the MSEP viewing area
after the parade and watch Wishes (and, by default, Celebrate the Magic.)
I'll assume that the CM's remove any ropes or other barricades for that area after the parade and those who
have been in the area can just "hang around" there until Wishes. (Makes sense.)
The person who reported that you could "stay" already had reservations at the Rose Garden for Wishes,
so (s)he went there to watch.
For me, the Rose Garden is not ideal for Wishes (steep angle too far to the right) and
even worse for Celebrate the Magic.
Although both of those shows would be quite watchable from the Rose Garden, both would be a better
experience seen from most places in the Hub.
If you think that you're a bit too close to the Castle, you will have plenty of room and time
to take a few steps "back" after the parade passes.
Lots and lots of room is made available RIGHT AFTER the parade passes.
It fills rather quickly, but anyone nearby can move to some prime real estate.
If I had MSEP FP+, I'd simply stay in that general area afterward for the other two shows.
Also, this method allows guests not to have to use up one more of the very
valuable and restricted FP+ choices on an "extra" viewing spot on the same night.