hi gang chen,
while for many uses, saving the data in a format which does not support all the features may be ok, it's probably not the case for DTP.
when you create a design for print, you rely on the program to reproduce it as you defined it. when saving in older version of the format, "random" items will be removed or slightly changed.
you probably don't want that!
also, since scribus is a free software application (which is not used in a corporate environment), nothing hinders you from updating to the latest version of scribus if needed.
you can always run several version of scribus in parallel. you just have to be careful and not open with a newer version, the files you want to continue to edit with an old version. and scribus will warn you when doing so!
have a nice evening
a.l.e