Robert,
The main thing the low scoring is telling us is that few, if any, of the President's Shield bowlers have bowled to date, so I would not get too worried yet about lower standards or harder lanes. Once the top guns arrive you will start to see the 650 plus scores appearing on the board. Although the lanes at Mt Gravatt are not easy, the good Junior bowlers are still scoring well there. For example, Matthew Smith, a member of the SQ Team, bowled a 904 (including a 299) in the Youth Invitational League at Mt Gravatt a few weeks ago and I think Andrew Nobbs (another SQ team member) shot an 899 in the same League at around the same time.
On the last occasion (1998) the Junior Nationals were held in Queensland (qualifying at Ashmore), you only needed 614 (Ross Sanson and Jarrod Pearce) to make the Open Masters cut and the top qualifyer was Brett Fox (SQ), with 693. The following year, on a much easier condition at Elizabeth (Adelaide), the cut was 660 (Terry Adams) and the top qualifyer was Dylan McKeown (NSW), with 739. (Coincidently, there was exactly the same spread, 79 pins, between first and last qualifyer in 1998 and 1999.) Last year, in Canberra, the cut was 631 (Brett Lacey) and Jason Twohill (SQ) was the top qualifyer with a 715 - a spread of 84 pins.
On this basis, it has got to be four years or more (if ever) since you needed at least 700 to make the Junior Open Masters cut. My guess is that this year the cut will, again, be around 630/640.