Winggo,
There are many ways to skin this cat. Your idea is simple, effective and inexpensive.
There are of course several afermarket VTA adjusters for Rega arms. Some simply thread on to the post, sit above the armboard and function exactly as you described. The Origin Live one is similar to your idea, though it's probably more expensive.
Others are thinner than a Rega mounting nut, which means the arm's base position is not raised up so much. Whether this is good or bad depends on how far your arm needs to be raised.
One of the cleanest designs is the Expressimo. It's not only quite thin, raising the arm by less than .5mm at the lowest setting, it also extends down the post into the mounting hole by 1/2" or more. This helps keep the arm post from wobbling about, but may require reaming out the mounting hole a bit.
There are quite a few others, including Pete Ruggle's VTAF (search ebay or Audiogon) and the Teres VTA adaptor. These are more functional, but of course they're more expensive too.