I would not waste money on a spare right shifter when you can buy new Centaur 10 shifters for $190, including a new cable set worth $50 (that must be used with these levers).

The new brake hoods are much more comfortable. The only warning though, is you want late '09 or '10 models that have the firmer click to the right finger lever. Don't buy early 2009.

Of course the other option is to buy Athena or Chorus 11 shifters, a chain and cassette and go 11 speed.

FWIW, the little you've done so far is peanuts compared to the rebuild process. It's simple the second time, but the first time can be frustrating - so many small details.

The new ultrashift levers are much easier to repair and should rarely need any repair with the new design.