What additional risks would I be taking with something like the Vanguard Australian Shares Index (VAS) that I wouldn't already be exposed to?
If you're in ING's Balanced option, the asset classes (including Australian shares) are managed passively by State Street, i.e. similar to Vanguard's VAS. The difference is with Choice Plus, you'll be responsible for your own asset allocation (split between Australian shares, international shares, fixed interest, etc.).
Would you consider indexes like this 'set and forget' or would you rebalance them yourself?
Quick illustration, if you start with $40 ETF A + $40 ETF B, and in a year, the former doubles but the latter halves - you end up with $80 A + $20 B, a significant deviation from the target 50/50 allocation. Rebalancing incurs transaction costs (brokerage) and involves selling the outperforming ETF A to invest in the underperforming ETF B (while counterintuitive, fits the adage of selling high and buying low). Should you not rebalance, your portfolio will be concentrated in ETF A which is likely out of line with your risk profile (e.g. say A was shares and B was cash). Right or wrong, financial planners generally recommend annual rebalancing.
Or perhaps more importantly: Am I falling for the 'think I know what I'm talking about' trap and I'd be better off in a generic balanced fund?
No two balanced funds are the same. ING's Balanced fund employs static allocation using passive investments (similar to VAS). Hostplus' Balanced fund employs semi-static allocation using active investments. Or you could use Choice Plus and decide on asset allocation, when/if to rebalance, etc. Fee-wise: Hostplus Balanced (at 1.4%!) > ING Balanced > Choice Plus. 12m performance to June 2017: Hostplus Balanced (13.2%) > ING Balanced (8.3%) - where would your own concoction via Choice Plus sit? Some fees are worth paying - Hostplus Balanced is notoriously expensive for an industry fund but it has delivered superior after-fee results to its peers.
"not many fund managers outperform the market average, especially when you take fees into account"
The active vs passive preference is not unakin to one's preference to risk taking. Simplistically, do you prefer a) low fees and similar returns to everyone else; or b) higher fees with the potential to both outperform and underperform. A compromise could be to split your mix, e.g. 70% passive and 30% active. Re Bogle, it's interesting to note while he initially founded Vanguard as a passive investing firm, it has since grown to US$4 trillion in asset under management, of which one third comprises active funds!
Everyone has their individual set of needs/biases/experiences, so expect a range of responses to your questions. An ideal planner would assess your needs, risk tolerance/willingness and (on the matter of investing) accordingly unbiasedly advice on the appropriate structure/product, asset allocation, active vs passive allocation, and appropriate investments within active/passive.