Under joint assessment you can potentially earn €72,800 between you at the standard (20%) rate. However if either earns in excess of €45,400 then the excess is at the higher (41%) rate. This is the Standard Rate Cut off Point. Your wife is going to suffer 41% on some income. You, on the other hand could pay 20% only. You could ask for the SRCOP to be split €42,800 to her and €30,000 to you. She would pay 20% on the first €42,800 and 41% on the excess over €42,800 and you would pay 20% on the €30,000. As regards Tax Credits you would have €1,830 each personal and €1,830 each PAYE credits. You could allocate the €1,830 personal credits to one or other of you or keep your respective amounts, the PAYE credit must stay with each of you as it is non-transferable. You need to complete the joint assessment application and nominate one of you to be the assessable spouse. That's just the person Revenue consider the first named for correspondence Tax Returns etc.
Other posters may have other ideas on this.