I would agree with Mike, as long as it is purely discretionary and you may need an employment contract to validate that it is, most lenders tend to add salary sacrificing to super back for servicing purposes.
As to whether it is worth 'sacrificing' today's dollars for retirement funds in 40 years will depend on your own goals. For those starting a career and early in their working life, my general preference is to build an asset base outside super that will provide flexibility and capital growth over time. Capital preservation is important in the early days of investing. For those older and closer to retirement, by all means contribute more into super if you have surplus funds to do so. Super is a tax effective structure so use it when it will give you the greatest benefit but you cannot access it until retirement or do much with it.
That said, having more in super for a longer period should enhance the compounding effect over longer years.