Since nobody has written it explicitly, I'll write that your "effect on quality" list looks about right, provided that each of the items meets certain minimum requirements. Of course, there have been many flamewars debating what those minimum requirements are!
My one quibble would be that room treatments can't fix a defective speaker design, so starting with the best speakers you can afford is important.
At the very least, you should audition the speakers -- in the showroom, if nowhere else. While room treatments and modern audio processors can compensate for some problems, they are not a panacea. Some speaker designs have problems that are immediately audible despite having a high price, for example.
Marantz SR7009/7.1.4/FH+TM/DefTech PM1000/LCR+TM amped