Locals who hit Gold Rush Days over Labor Day Weekend will notice some changes in Old Sacramento.   New business activity including historic building reconstruction is underway. While the addition of new ventures hasn't totally offset the loss of others, tourism revenue for 2009 seems to be holding steady with 2007 and 2006, said Melissa Martinez, executive director of the Old Sacramento Business Association, a business improvement district. "We're staying steady in tourism," said Martinez. "That’s a really good sign." In 2007, retail businesses brought in $2.25 million in sales tax revenue, about the same as 2006. Tax receipts dipped by $129,000 in 2008 — primarily due to the I-5 re