Get that finger out of my face!
Top-coating the dice would make me worry that their balance would be off. If you don't coat evenly, you may have a die that rolls one way more often than not.
Can't really imagine wearing out the dice, but I guess if you did, might be worth your while to purchase another set from the publisher.
As long as it is a thin coat, it shouldn't throw the balance off in any noticeable way (The additional mass added to each side by the thin layer of lacquer will be much less than the mass of the die to begin with, and since a coat will be added to each side the difference will be offset almost completely). The only problem I could see is the lacquer not drying flat and changing the shape of the die, which would affect the randomness of the dice rolls.