How can one combine religious observance with enjoying life, such as traveling and recreation, and reconcile saving with spending for the sake of Allah? And is it better to save money or to spend it to avoid its loss to heirs?

A Muslim should observe moderation and balance in their life, striking a balance between the needs of the soul and the body. Adherence to acts of obedience does not preclude permissible recreation, and a habit can be transformed into an act of worship with a righteous intention.

As for spending, it is sunnah (definition) for a Muslim to spend and give charity in the path of Allah, and to leave behind enough wealth to spare their heirs from begging people. It is not obligatory to save a large amount of money, nor is it preferable to spend all one's money to deprive the heirs. Rather, one should be moderate, and what is left for them is not considered a loss if one has fulfilled their religious obligations.