2. Changing the oil at this point will probably mean more cost to you without improving fuel economy. I'd hold off until the 1 year mark since your last change. That's what I've read for the max amount of time to go between changes.
3. I think the amount of electricity DRLs use is small compared to what the rest of the car is using. My Civic uses about 55 Watts (about .07 horsepower) for both lights. If you want to test the impact, you may have a fuse for them that you can pull. Try monitoring the voltage with the ScanGauge. If it's up around ~14, the alternator is running. If it's down at 12.5 or below, you probably have a smart alternator that doesn't run continuously. I pulled the fuse for the DRLs in my Civic, but didn't see a difference so put it back in after a couple days. Keep in mind that you'll be less visible to other traffic in some situations without the DRLs.
5. No experience with a Corolla, but make sure you monitor coolant temps on the ScanGauge once you get something in place. My Civic can't do long highway drives (>50 miles) with my full radiator block in place. Here's the only thread I've seen for a grill block on a Corolla. I don't know how it's grill compares to your XRS.
http://ecomodder.com/forum/showthrea...auto-2300.html