Since one can benefit so much from practicing Metta, can it also helps improving one's luck?
Luck is preparation meeting opportunity.
As discussed in this answer, Metta makes one dearer to others, strengthens one's mental concentration, brings peace to one's mind, grants protection by the Devas (gods or angels) and provides protection from harm (e.g. fire, poison sword).
So, if you can have a better relationship with others, then this improves your social networks. If you have better mental concentration, then you can correctly identify opportunities that appear before you. If you have protection from harm, you may be led away from unfavourable situations.
Metta therefore, forms part of the right preparation that will allow you to seize the opportunities that come your way.
However, we should bear in mind that worldly luck is not permanent (anicca) and is part of the suffering (dukkha).