Are there any recommendations or guidelines as to when a set of road tires should be replaced? I typically put on 100-150 miles/week from May to November. I check the tire surface before any ride and don't see any obvious problems. I have had occasional flats but am not experienceing recurring problems. I will be going on a 350 mile 5 day outing through some serious mountains next month and want to be sure the bike is in good shape.
This is rule of thumb only. But you should get 1500 miles, more or less, on a rear tire. When changing, rotate the used front tire to the rear and put the new tire on the front.
The front tire being non drive doesn't loose much tread.
Of course, that is all rule of thumb. You should periodically check your tires (like before each ride). Cuts and gouges and abnormal wear (flats spots due to hard braking-skidding) should be double checked and may necessitate earlier tire replacement.
My rear has about 2,500 miles on it (Conti UltraGatorskin), and I notice that the surface seems to be getting "squared off" (don't recall that I've skidded on it). I'm taking this as a sign although it otherwise performs well.
You did not say how many miles are on your current tires. If you going on a trip you could install new tires for the trip just to be safe, and carry one of the old ones as a spare. Also make sure you carry a spare tube (protected by it's box or wrapped in plastic bag) and patches...that should be a no-brainer. If your current tires are the folding kind just fold the tire as small as possible and stand on it to get it to flatten as much as possible then put a couple of heavy duty rubber bands tightly bound around the tire to keep it flat so you can carry it on the bike.