Yes, this sounds right - with the exception @JohnRice noted above, if you choose particularly hard to drive speakers you may need to get an amp for them sooner. That's growing less common these days - but there are some older designs like John's Thiel's and old Apogees that are absolute power hogs.
Used speakers are purely a bang for the buck play - there's no other reason. That said, a very expensive audiophile speaker that's 15 or so years old can be had for a fraction of its original cost, and will often sound worlds better than modern cheap speakers. Although marketing departments...
I tend to give this advice to anyone who asks me about what to upgrade next. In order of importance for audio (where your $$ should go first):
0) MiniDSP/Calibration and DSP optimization of what you already have
1) Better speakers
2) Room Treatments
3) Additional or Better subwoofers