Some time ago it was noticed (http://lists.gnu.org/archive/html/emacs-devel/2012-03/msg00371.html)
that coccinelle tool (http://coccinelle.lip6.fr) might be useful for get rid of the GCPROs;
but it seems that this tool opens a lot of other opportunities. For example, attached patch was
generated with the very simple "semantic patch":

@expression@
identifier I1, I2;
expression E1, E2;
@@
(
- XVECTOR (I1)->contents[I2++] = E1
+ ASET (I1, I2, E1), I2++
|
- XVECTOR (I1)->contents[E1] = E2
+ ASET (I1, E1, E2)
|
-XVECTOR (I1)->contents[E1]
+AREF (I1, E1)
)

and following minimal manual intervention, so I suspect that more useful cleanups may be done
with this tool.

Dmitry