Water condtioners- are they absolutely necessary?

Given the recent hulla-bulla over trace elements like potassium, calcium,
zinc and all, I've started to worry about not having enough of these trace
elements in my water as the only water conditioner I use is anti-chlorine
crystals during my water change.

My question is, are water conditioners absolutely necessary? I understand
they don't come cheap. Prices range from the cut-throat Duplagan to the
equally expensive Tetra ones, going to ones bordering on gimmicks like
"Geoliquid" (which I actually tried and burnt a hole in my student budget).
THey all claim to contain special chemicals which calms the fish and contain
trace elements necessary for plant growth, simulating nutrients found in
natural water sources. But my fish and plants have been ok so far without
any of these and I would like to see if you guys, who like me, do not use
any of these stuff, have any trace element deficiency.

I currently use Duplaplant and Duplaplant 24. Would these be enough to
supply all nutrients and trace elements necessary? I'm in fact considering
switching to Tropica's Master grow given the increase in Dupla's prices (yet
again). Would I be missing something if I do?
Calvin Chin