I live there. You might try my web site, Santa Barbara Hikes (google it.) Some people have been there recently.
They don't maintain the trails very well in the Los Padres. This affects your ability to go in very far.
A good first-timer overnight is to hike the Manzana Trail, which is a well-maintained trail. You can go upstream out of NIRA campground toward the Narrows or downstream toward the Schoolhouse. Both are nice trips.
Both are along Manzana creek and it will have enough water for you. There may be dry spots this late in the year, but it's been a good year for water so you should not find yourself without water.
Heading toward the Narrows you can camp at Fish Creek only 3 miles from NIRA or the Narrows which is about 7 miles in. You may find little camp spots along the way. After the Narrows, they've recently worked the Big Cone Spruce trail so you could go up to Big Cone Spruce camp. Otherwise, the Manzana trail rises up some switchbacks into a wonderous area called Whiteledge. There should be water at Happy Hunting Ground and Whiteledge Camp and at the other camps further in. South Fork Station is probably as far in as you could go for an overnighter. The trail is less well-maintained the further you go past Happy Hunting Ground.
The Schoolhouse is nice, too. It's a relatively flat hike. You go downstream and there are a few campsites along the way, one is 1 mile in (Potrero Camp), another is about 3 miles in (Coldwater). There is an old Schoolhouse above the campsites at the Schoolhouse camp and you will be at the confluence of the Manzana and the Sisquoc river. If the Manzana and Sisquoc look dry, there are usually some stagnant pools downstream on the Sisquoc.
It has been a good year for water and I haven't heard any reports of it being dry. Last time I was there it was a wet hike down to the Schoolhouse.