Understood. I've never dosed and have always done 20%/month. In my current 60g cube and the salt at roughly $60/200g the water changes are quite inexpensive. It's simply that I prefer not adding anything. Keeping it simple means that should something go horribly wrong, figuring out what happened is made simpler. I'm a subscriber to the Keep It Simple theory on life.
The problem with this is that as you get more acros and they start growing faster and faster, they are going to use up a TON of Alk - more than you can keep up with only doing weekly water changes. You will have to start changing the water 2-3/week and changing larger quantities of water. If you don't, you will be causing large swings in alkalinity by changing 20%+ a week killing any sensitive acros. Really, if you want to keep large acropora colonies in small tanks, you have no choice but to dose (2-part, kalk, or ca reactor) or be doing daily water changes (which is far less simple than just dosing Alkalinity, Calcium and Magnesium) - because to get consistent results you will need your daily water to be spot on - which means testing it for pH, salinity, temperature, alkalinity, and calcium.
In my tank right now, with the SPS taking off, I am going through around 1.84dkh/day of alkalinity. In order to not lose my acros from alkalinity swings, I would have to be changing the water at least once a day to bring that alkalinity back up and that would still be very stressful because of the be alk swing. You can get VERY pure 2-part additives with only Ca and Alk and manually dose them - this way you are still keeping things simple - no more equipment to fail and dose once or twice between water changes.
I went with a doser so it could dose small amounts 6-8x per day to keep the alkalinity within 0.1dkh. Since going that route I haven't lost a single Acro colony.
It isn't so much the expense of salt (which is fairly cheap all things considered), but the stress you are going to be putting on your corals with alkalinity swings if you can't change the water ever day as you start getting bigger, faster growing colonies.
Edit: I go through so much Alkalinity because I only have around 22 gallons of water volume between the DT and Sump and have 12 different acro colonies that are all settled in and growing like mad, 3 monti colonies, and another 8 larger frags on the rack and are in various states of adjustment, some fully adjusted to my tank and taking off as well.