Well, none of my three kids had issues with basic math and we never did math drills at home so take my opinion with a grain of salt. However, I do think that it is important for you to help your DS maintain at least age/grade appropriate basic math skills so that it will be clear as he ages if he does have a disability in this area and also to avoid loss of opportunities that may require basic math skills.
Having said all that, I also believe that you should not hold your DS back from soaking up new concepts just because his basic math skills are not established as yet. My inclination would be to leave it up to him as far as which concepts he wants to explore and just be available to assist when he requests help. It sounds like your DS has interest in math, which may actually provide incentive and opportunities for him to gain proficiency in basic math.
For what it is worth, with the exception of kids who were heavily drilled (i.e., kumon, etc.) I have never observed a child who wasn't more capable of understanding math concepts than mastery of procedures. It is sort of analogous with listening comprehension versus actual reading comprehension, where it would not be unusual to see a gap of a couple of years or more, especially in the earlier years. I believe this difference partially underlies the philosophy driving the spiraling in elementary mathematics: kids can understand concepts far earlier than they are ready to master the sometimes relatively complicated procedures.
