Veno wards should be used with foresight, not as a kneejerk reaction. Granted, sometimes you will need to throw one down in front of you so you can see someone running away, but that's about it when it comes to using one at the spur of the moment.
What you should be doing with them is place them as preventative measures. This means the following:
1. Putting Veno wards at places where you'd normally put a regular ward... in case you don't have one. This is gank prevention. Put as many as you can all over the jungle to protect your lane from almost everything except smoke ganks.
2. When you see an enemy push incoming you should start stacking wards in front of your tower. Don't put individual wards here and there, it's pretty useless and just feeds people gold. But if you have 7 - 9 wards stacked at your tower, chances are they will never be able to push without a serious dive on their part. Furthermore, you need such a huge clump of wards to clear the incoming creep waves. One or two won't cut it in the least.
3. Similarly, when you're planning to assault a lane, you should prepare by placing a gigantic clump of wards somewhere out of the tower range and beyond where the enemy can easily kill them off. This gives your team a place to fall back to as well as a great place to fight. And it pushes the lane really hard.
4. Lastly, if for some reason you want to seriously piss off the enemy. What you should do is after you manage to kill an enemy laner, start plunking down wards in a giant mass in the middle of the lane. When he comes back he will be completely screwed. For obvious reasons you can't really do this while there's an enemy in lane as he'll kill them as they appear.
In any case, if you're running around spamming individual wards for no real purpose, there's no point to it and yeah... you'd be just feeding the enemy gold and exp. One or two wards also do barely anything in actual fights. Your autoattacks are probably more useful. If you're standing at the edges of the fight, then you can throw them down if you want. I just wouldn't recommend it in any situation where running is better.