In my opinion nowadays leveling up the magic level has become more important than in the past years for paladin because of the imbuements of vampirism and mana leech. The most damage you deal, the most hp/mana you are getting in exchange; and for paladins it makes a difference when you use your spells and expansive runes properly: diamond arrow + divine caldera + diamond arrow + expansive rune. This additional hp you are getting, in addition to your healing spells (which will be higher as well because of your magic level) can stay you alive and spend less supplies.
Second reason of leveling up magic level is that unlike training with exercise bows, it takes less rods/wands to increase the magic level (for me for example: I need almost 3 times the amount of rods that I use, to increase the same proportion of distance.