If you are just looking to dive more, then just go dive more...there is no reason to renew/retrain at the DM level or bump up to instructor.
Consider that there are agency fees, insurance fees, you need your own gear, plus gear for your students unless you are working through a shop or a dive operation that provides gear for your students. You do not want students using your personal gear that is not dedicated to your business of teaching...that adds risk/liability.
I can't speak for the land down under, but here in the USA it highly recommended that one establish/register themself as a LLC if they are going to teach or DM, this makes it so ones personal assets are severed from the teaching business aspect and you would only be personally liable in a lawsuit if your personal actions were found to be negligent....registering as an LLC is not particularly expensive, but it is an additional expense.
My recommendation is to put your old DM certification card in a scrap book, present yourself as an AOW diver (perhaps with a nitrox cert), and go out and enjoy diving with whomever/whenever.
There was recent discussion on SB, perhaps it was in one of the private groups, that indicated some folks were planning to let their teaching cert lapse at next renewal due to the ever upwardsly spiraling cost of agency fees + professional liability insurance fees, among other additional reasons.
There is very little benefit to being an instructor/DM....as others have pointed out, the pay is barely enough to cover one's expenses, and at best one MIGHT get "key man" pricing if you are working for a shop and the owner decides he/she wants to extend that discount to you.
Compare that to being certified as a instructor under the Professional Ski Instructors of America / American Association of Snowboard Instructors (PSIA/AASI), where the certifying/training organization is partnered with about 70 different companies that offer deep discounts to certified instructors who maintain their membership status. In addition to that and even more important are the abundance of continuing training oportunities as an instructor under the PSIA/AASI wholeheardetly geared towards making one a better instructor. Continuing education is requirement to maitain credentials, and the training seminars and clinics are by far worth the expense.
Unfortunately there is nothing comparable in the recreational diving world for dive pros....which is sad and a bit confusing given the high risk and potential liabilities that teaching folks dive presents.
This past year will probably be the last time I renew my PADI membership as a DM...its just not worth the cost.
I am greatful that there are folks that want to be instructors, but I would never recommend it.
-Z