Why spend more money? Why not just move your existing dropchecker around to several places throughout the week and build up a profile of the various locations?
Because I already own quite a few drop checkers, so I'm not spending money, I already own them and have done for many years. Also moving them around the tank to try to 'build a profile' will only tell you how much CO2 there was at that position at one particular time in the life of the aquarium, this can and will vary, as you well know aquariums are dynamic, even with the best flow etc you are still going to get a significant amount of variation. By placing a drop checker at either end, I am able to get an idea of the CO2 levels at different points at the same time, which helps me to build a better picture of what the currents are doing within my aquarium at any 1 time (even if it was 1 hour ago).
I also think that you completely missed the point of the 'not broken' comments. I am sure that this wasn't meant to suggest that drop checkers are perfect, but rather amongst drop checkers the design we already had is about as functional as a drop checker can be. Anything else is just a gimick, bells and whistles. I am sure that the new Cal Aqua ones will sell by the load however, as there will always be people who actually WANT to pay more than they need to, under the illusions that the old addage of "you pay your money, you make your choice" is actually always true, ie. it costs more so it must be better.
Now if they really want to improve upon the drop checker design, things that are flawed include the need for a constant light source of a certain spectrum (the green I see in mine may look totally different to the green I see in yours, purely because your lighting is different), glass ones are also lacking in a decent background upon which to view the colour (look through one towards a green background for example and it will look greener than it is).
I use my drop checkers as a reference point to check that I am not over/under dosing with CO2, within that range if my plants are growing well and healthy I consider the levels, and flow throughout my tank, to be satisfactory. As an aquarist I don't need pin point accuracy. Drop checkers are proven to work for aquarists, at the end of the day an aquarium rarely need lab conditions and accuracy.
As to buying a pH meter, what ever for? My fish, shrimp, and plants are healthy and happy, and have been for many years, so why would I worry about my pH? I test so rarely that spending money on an electronic meter would be a real waste.
Ade
PS. My glass drop checker cost me under £3, hardly breaking the bank.