Joe?

Drill a new set of holes between the existing holes the size that you want for your bench dogs. You can use the existing holes for jigs you might build in the future for clamping and holding work pieces when the vise just won't work the way you want to hold the work.

 

What Mike said.
Or, you can get larger bench dogs.
Or, you can plug the holes, and drill new holes.
Or, you can build a new bench. :sarcastic:
I'd probably go with what Mike said.

 

Three things come to mind. The first is if have a lathe make a piece of dowel that will fit the holes. Second place a piece of 1/4" thick mdf over the hole and with a muli-tool like they sell at HF cut into the 1/4" to get an exact fit then chisel out the insides of the top. Last cover the top with a piece of 1/4" hdf (aka masonite) which will give you a longer lasting surface and then re drill.

 

What Mike said. I enlarged my holes to 7/8 inch so I could insert 1/2 inch pipe to clamp stuff to the table. I also cut the tab off several Harbor Freight bar clamps so I can use them for the same purpose.

And I made some bench dogs out of 7/8 oak dowel, then cut some 1/2 inch plywood to fit over the dowel to make a flat face. Cheep, yet effective.

 

I've had to fill errant holes in MDF and all I do is to use a holesaw to cut out a circular insert larger than the existing hole. It's then a matter of either sanding down the insert a bit at a time to fit the hole, or enlarging the hole to take the insert. I usually use the former method. The insert is then glued in place with PVA glue, Titebond, etc. A quick sand down with 400 grit and you wouldn't know there had been a hole there. You can then drill new holes, even part way across the the insert.

 

If you decide to fill the holes, drill them out to a larger size that you can buy doweling for. You didn't say what you had used to drill the holes with or the method you used that caused the holes to turn out badly. You cannot use a spade bit for drilling the holes. Your best bet is probably an auger bit, but the auger bill will probably cause a lot of tearout at the beginning of the cut so I would start a hole with a holesaw or Forstner bit. You can drill a hole through a 4 x 4 with a drill press and use it as a drill guide to keep the hole vertical.

 

$80?...Seriously?!
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I got all excited until I noticed the price.

On the oversized holes part, you didn't mention how much over-size they are. Would a short section of brass tubing inserted into the existing holes resolve the problem?
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