There's no need to focus on leveling it anymore. As long as you've unlocked desynthesis and the needed DoH class, you'll be able to desynthesize the item.

The advantage of having it leveled to the recommended desynthesize level is you will usually get more materials back (so if it takes 4 of a material to craft, you'll usually get 2-4 back instead of 1-2) and a much greater chance to get back one of the "rare" items like demimateria or Sublime Solution.

As you say, gil is plentiful so profits that can be made from desynthesis don't seem like much but for the players with less gil it can be helpful. The way quick ventures have flooded the MB with items, you can make a profit even without desynthesis at the correct level if you pay attention to prices.