> That's no problem, the problem is changing it later, which one can
> do with PSFRAG.  Of course, it could be regenerated, but that's what I
> want to avoid, especially if it means reading in a lot of data etc.
> Also, perhaps someone else, who doesn't have the data, needs to use it.

That is a very important issue; thanks for clarifying it here.

To meet such very real needs, any system for combining typesetting and
graphics needs to make the distinction betwen them clear and preserve
this distinction in the various user interfaces.

Of course, there are cases, especially in teaching materials and
adverts, where the local structure does mean that there is no clear
distinction between the two, but there is also a large area where the
distinction is clear.