Ok, I know this is probaly a dumb question to most of you but I'm just curious. I don't usually bring my bike above 140km/h on the highway, which is pretty much cruising speed on the highways around here. Just saw a comment on another thread regarding speed and wheel weights and I'm curious about the risks associated with not having them.
If your wheels aren't balanced, you'll have handling problems. IMO it's more dangerous on a bike as opposed to a car, but the same physics applies nonethelesss.
If you haven't noticed vibration so far, you may be lucky. If it is bad enough you'll get uneven tire wear, bad shake in the handlebar or seat, and generally uncomfortable and dangerous riding at the speeds you quote.
If you're concerned, consider buying another set of tires and have them balanced properly. My rear tire carries close to 100 grams, and a little less up front -- quite a lot I thought and hate to loose them.