Yes over time it will. I would say it is worth it to have a PSU that runs as efficiently as possible. This is a good indicator of power supply component quality. Don't skimp on your PSU, there will be other ways to save money.
I'm going to get a new power supply soon, and I've always wondered if 5% more really makes it worth paying an extra $20-30 for.
It depends on if you are paying for your own electricity bills.
Assume 200w average usage, and 5 hours per day. That's 1kw hour per day. At 10c per kwhr 365 days per year, you have a cost of $36.50 per year for electricity.
That's only a couple of bucks savings which will take several years to make up. If your numbers are significantly different, then perhaps it is worth more.
But, a more efficient psu will run cooler and quieter which is worth a bunch to me.
Like JSC said, the higher efficiency units are usually higher quality units, i havent seen a review of a bad 80+ silver or gold unit. Also keep in mind that higher efficiency means that the PSU is producing less heat that it has to deal with so its fan can run less.
You can do some quick math to see if its justified, average DC load of 300W, lets say 8 hours a day, all year long, with one PSU thats 80% and another thats 85% efficiency.
System with an 80% efficiency PSU draws 375W from the wall, 85% efficiency draws 353W from the wall. Thats a 22W difference per hour, 176W per day, 64.24kWh per year, and at 10 cents/kWh thats about $6.50 a year so after 3 years it pays for the differences.