Best Used Speaker Under $4,000 w/ Respectable Lows

"I tend to treasure transparency, neutrality, high end extension, speed, DYNAMICS, and tight driver control / integration in my speakers and leave bloom/coloring/musicality to the amp. I also prefer speakers that play very well at low volumes with medium power amps."

Transparency
Neutrality
High end extension
Speed
Dynamic (contrasts)
Play at low volume without losing the above

The latest Merlin VSM-MM or MX might be what you are looking for. They certainly excell in all the areas of your criteria, check the archives and reviews. You will get the best customer support in the business whether you buy used or new. Bobby Palkovic is always there to help you every step of the way. In any event you should not buy anything without listening first.

There are many speakers that might suit you and there is nothing clear cut, one man's love is another's loathe.
Speaker choice is a very personal choice, more so than anything else in the chain IMHO. You'll get plenty of suggestions but you really have to do your homework. Good Luck and welcome back!

I had a couple pair of Merlin vsms and the mme. I loved the mids and highs but thw lows were a little weak in my main room which is 20 x 24 x 17. I used 2 jl 113's with them and that gave me some good punch.

My 2nd room has a 9 foot ceiling and they sounded much better there and i didnt need the sub.

I do listen to a lot of dvd's, concerts and movies and the merlins were great in that arena.

I suggest you check out the Abbey speaker designed by Dr. Earl Geddes. They are amongst the best speakers I've heard in my 30+ years in this hobby/obsession. When you take into account price/performance I put them at the top of the list. They punch all of the buttons you listed, except being full range. They are flat to 50hz and then roll off at 12db per octave. You'll need a sub or two to get the low end. IMHO, after having owned several pairs of full range speakers, the best way to get flat low frequency performance in most real rooms is multiple subs located asymmertically in the room.

While I've not heard the Merlins or the Salk's I can say they also have a strong following and appear to be a great value.

Usher Audio Tiny Dancer Mini One

I'll second the used dunlavy's.   Hard to beat a pair of sc=iv's or larger, full range and they just do everything well, fairly efficient, not sure what your amplifiers specs.   They can run on middle of the road  power , really shine with nice amplifiers.   John dunlavy understood speaker and crossover design on a very awesome level.