A great find - the then bumblies Julian and Simon managed to bolt and, eventually, send some classic steep sport routes.
Be aware that most routes at this crag rely on one bolt keeping you off the deck, even when you're well up the pitch. If a bolt breaks or pulls, or a biner unclips, you're toast. Bad belaying pretty much guarantees groundfall potential as well - this has already resulted in a number of big plummets, near groundfalls, and actual groundfalls even from quite high on routes (thankfully with surprisingly minimal injuries, so far).
The climbs are great - but it's your own responsibility to decide whether or not to climb them.
Mobile coverage is poor to non-existent from the car-park to and at the caves. However there is coverage from the top terrace at Pygmy Terraces near the car-park so there may also be coverage if you scramble to the top of Millenium.
Note the road from Buandik campground is closed in the cold wet months (from about Jun/Jul) to protect the road itself, and is scheduled to open at 'October' 31 each year. The Parks Vic website has a link to the 'Grampians' Road Report, which gives current road conditions and road closures. If the gate is closed keen climbers can still get there simply by walking up the road from Buandik (about 1 hr total). If the gate is open, drive up Goat Track from Buandik for about 1.5km. This crag pretty much completely occupies the top of the hill to the right (south) as Goat Track reaches it's high point. 2WD cars can be coaxed up the hill...but a bit of clearance and/or 4WD is certainly desirable to navigate the large water bars and steep loose rocky sections (softroaders will be fine). When the road reaches a saddle at the top of the hill and starts to drop for the first time, there is a parking bay on the left (north) side of the road. The walk-in starts directly opposite, you can't really see the crag so just follow the well-formed track. The view of the crag in the first topo below is from the intersection of Goat Track and 'Victoria Range' Road - if you end up here you've gone too far, go back towards Buandik until you reach the saddle.
Goat Track is equally passable to/from the east (i.e. for suitable cars), and joins up with Syphon Rd at the eastern foot of the range. This way is probably a bit quicker if you're driving to/from Halls Gap but involves a bit more rough driving. Great views though.
The walking track is well trod and easy to follow, and initially heads away from the road but then starts veering left and contours the hillside, until you reach the 'Five Spice' cave after about 10 minutes.