You mean the spark plug tube seals and the valve cover gaskets like:
http://www.rockauto.com/catalog/moreinfo.php?pk=128852
Definitely
reseal the semi-circular plugs. You can use Permatex Ultra-Black or Ultra-Copper RTV. Dollar store high-temp sensor safe RTV also works, for a dollar.
Clean off the old RTV from the plugs with a small screwdriver or a wire brush. Make sure the surfaces are oil-free so the RTV can stick well. Use alcohol and paper towel. Stuff some paper towels in the area to catch old RTV you're scraping off the cylinder head. Then also apply dabs of RTV at the specified spots when installing the valve cover gaskets.
Change out the
PCV valve and grommet. The grommet hardens and becomes brittle. So it'll probably come out in pieces. That's why it's best to do this while the rear cover is off.
If you are changing the spark plugs try
NGK Iridium-IX. Get new NGK
spark plug wires if you need them.
Since you're very close to the water bypass hose under the low manifold, maybe change that out as well. Remove the bolts of the lower manifold and tilt it up without touching the fuel rails.
If changing the timing belt it's a good time to change the valve stem seals as well if you have over 120K miles. But special tools are needed.
Clean the IAC while disassembled (1MZ similar):
5sfe IAC Removal (lots of pictures)
Linear Mode
