Before you change anything, I would at least recommemd doing an informal flow rate check. Use a 5 gallon bucket or a 2 liter bottle.
I kind of like the redundancy of two pumps in series, but I wouldn't suggest that until you at least did a rough flow check. The EK spinner could just not be very sensetive. Then you would be spending $80 for no measurable gain. If you want to upgraade pumping power, just don't do for big performance gains. At one point I had three loops in one system and as a side experiment strung the whole mess one one pump and the temperature was basically the same +- a couple of degrees.
I would only do it for fun or so you can see the spinner moving faster. I had three loops so I could run three different fluid colors..I feel better that I've tried that now..