With regard to the speeding up to 250 after the fix, I was very surprised that jets would do less than 250 prior. I was expecting a 250 knot descent and than if that was not enough a request for vectors/holding. I didn't even know a jet could do 210 on descent, I was always taught 250 was a minimum we could assign, if we had really messed up we could ask nicely for 240 or maybe 230.
The minimum speed depends on altitude & weight, along with type to a lesser extent. Generally, the lower you get the slower you can go - down to minimum clean speed, which is around 200-210 kts at typical landing weights on the NG. (taking flaps will get you slower, but can't be used above FL200 & that is the last thing we want to do anyway!) Generally you are light when arriving & in an NG, light enough to get back to 210-220 kts somewhere around FL300. Above FL300 would require a bit more speed. It depends a little on the particular pilot's (read captain's) pucker factor or simply personal preference, and also on turbulence, etc. The B777 wasn't too bad either if I remember correctly, with slightly higher speeds, maybe 5 or 10 kts more.
Constant speed descents are easier for the FMC to calculate & fly in VNAV, which is the way the boss likes us to fly it. However, it can handle one or two speed reductions, preferably over waypoints (easier to program). Once you get speed increases or vectoring, you are off the 'path' & then it is back to manual calculations. It can be done & is really no bother to most, it just offends our sense of economy & passenger comfort.
Once everyone gets their heads around what has to be done to move large volumes of traffic, then you will get a better response to any restrictions & less complaints. Guys are still trying to hang onto economy. Perhaps a couple of months in Dubai would educate them & they would see that it is still pretty good in this neck of the woods.