FWIW I haven't messed with the stock coolant thermostat on my 1991 CRX. However, I do have both a variable (set moderately high) thermostat on my fan, and currently (in the middle of the winter) a 90%+ grill block (the block is only around 2/3 in the summer).

And yet, I too notice that my CRX will usually take at least 5 miles (sometimes more) to fully "warm up". So, since my experience is similar to the others, I guess it's just the nature of CRXes. Oh well.

NOTE: My grill block helps a LOT in how fast it heats up, as well as how well it keeps it's temp after heating up. Yes, the CRX still heats up slower than some other cars, but it still heats up a lot faster (in the cold winter) than it used to before I blocked as much of the grill as I am currently doing. So if the OP hasn't yet gotten a grill block, now would be a good time. Just keep in mind that a grill block is a balancing act. While it helps warm up the car quicker (more heat in the cabin, AND better FE after it warms up), you still don't want the car to overheat (which it can easily do if/when you block too much of the grill, and then take a long drive). So keep in mind that things are a balancing act, and watch that temp gauge...

Grill block has been in place.

CRX = Less heater. Roger that.

Oh, well. Commencing sucking it up and getting on with life.