IMO increasing the bore of the TB is only going to be worth while if the engine is extensively modified and requires greater flow. Like running higher RPM, or if the head has been ported and flow benched and the numbers say the TB is restrictive.
The stock TB may be on the small side, but our motors aren't high revers, and I'm sure it's not because the TB is holding it back either. There's also something to be said for keeping a good velocity through the TB. You just don't want a pressure drop across it restricting flow. My rule of thumb is to never cut or machine anything untill you're sure it needs it. So, my advice would be to wait and open it up when you're far enough into modifications to really need it.
One thing you may want to try though, is a junk yard search for an alternate TB that would work and has a larger bore. That way you'll know how much of an effect it has without bastardizing your stock TB. Then you can always go back if it doesn't work out.
