No, I do not expect that cutting benefit fraud will result in a tax cut. Howver, it may actually prevetn yet further stealth tax increases, which results in much the same thing - more money in your pocket than you would otherwise have.
Here in Spain, direct taxes are quite high to cover the cost of the social security system, but that is mostly offset by lower indirect taxes (petrol is 45p per litre and beer, wine and spirits are almost free with local supermarkets charging less than the old "duty free" shops used to!).
There is plenty of annecdotal evidence that having an ID card reduces fraud - not just benefits but also credit cards - and may have some scurity benefits. Mind you, ETA seem to still have a pretty free hand.
ID is not the answer to all problmes but is a useful tool along with other checks and procedures.
I'm al for ID cards - the sooner the better .