For 2012 married tax credit at 20% is 3300, (income to €16,500 tax free).
Paye tax credit is limited to 1650 at 20% and is specific to each earner.
For you €8000/5=1600
Limit for your spouse 1650
Tax credits 6550, covering income up to €32,750
You may have other tax credits that I'm not aware of.
The current level at which the high rate of tax kicks in is €32,800 for an individual.
The tax on your deposit income is limited to Dirt, (currently at 30% I think).
Things will obviously have changed by the time you draw the State Pension,but using current figures, you would have Paye income of €20,000, your wife still has €10,000 at that point. Joint income €30,000. Tax credits married 3300 plus Paye 3300 means you can have tax free income five times this, €33,000.
You might think you would fall under the exemption (currently €36000 for a couple where one is over 65) but your deposit interest would bring you above the limit, and Dirt would still be taken from your deposit interest.
There are special term savings products, where for a 3 year term, up to €480 and 5 year term €635 interest per person would be tax free. With the amounts you want to put into a deposit account, it wouldn't make much difference perhaps. Also the banks may offer lower rates on these products, but it may be worth reading about, and having such an account as part of your strategy.