Do I really have to wire red-to-red and black-to-black?

Yes. Speakers and amplifiers are coded red (positive, +) and black (negative, -) for a reason, and that is because the speakers will sound best when they are in-phase.

Let's say you accidently wired one of your speakers backwards. This will cause one speaker to be "out of phase" with the other one, so they will not be producing the same sound at the same time. In fact, depending your room arrangement, they may actually be cancelling each other out somewhat, and making your sound significantly worse.

So yes, always wire your speakers according to their polarity for the best sound.

bzzt.

yes because you can get power from the wrong wire such as your ground and most likely overheat your amp plus you wont get the proper sound the wires was set up for

Now I dont think people should make this more complex then it is. You can think of speakers as batteries. If you have a amp with one speaker then yes positive to positve and negative to negative, but if you have something like a 4-12 cab. then you can wire it (this is where you think of batteries lol ) positve to negative from one speaker and so on so it makes a chain around your speakers kinda like putting batteries in a radio. Hope this helps ya, If not......well i tried. :D

As far as actual "red-to-red and black-to-black"..... No you do not. It is BEST to do it this way so that none of the speakers are out of phase with each other. You could wire them red to black (or black to red if you want it that way) as long as ALL the speakers are wired the same way. But to keep the confusion down it is BEST to wire them by thier color coding (or by polarity if no color coding is present).