Keeping it simple is great when you are starting out. However, as you get into more difficult fish and especially corals things do get a bit more copmplicated. At some point doing water changes to keep alk and calcium at the proper levels becomes much more expensive than dosing. The more stony corals and clams you put in a tank the faster these elements are diminished.
As for quarantining you new fish, I believe that strarting with your very first fish and QT'ing every single fish from then on is just good husbandry. If you cant afford a small extra tank with a filter and heater then you really don't belong in the hobby. You truly are playing russian roulette by not doing this crucial step. I've been there. It is devistating to lose all or most of your fish because you skipped this one step. The only time you really need a large quarantine tank is if you skip the qt and end up having to treat all your fish at once.
This is my experience, you can do what you want, just try to remember that the animals we keep in our tanks are living things.
Some really good responses so far but must say that I totally agree with this above post.
Cheers, Todd