I think the CSE was released as some form of bone for ASM programmers who were starving for a TI color calc with built-in ASM support, since the Nspire is so locked down. Also, since the Z80 line doesn't want to die in popularity, they probably took advantage of it as well and added a color screen to attract more people.

I think you still made a good choice by buying this calc, because look on ticalc.org how many POTY entries there were for it in 4 months compared to 83+/84+ entries in 12 months. On top of that, some 84+ entries were programs from several years ago being retro-actively featured (Illusiat series, for instance). However, speed-wise, the monochrome model is obviously better, while memory/screen-wise, the color one is better.

There is also the problem about the Nspire CX being more expensive in most countries. Over here, when school starts, you can get the CSE for $129.99, while the Nspire CX never goes under $149.99. In USA, I think the prices are pretty similar. Some parents will probably try to go for the lowest price possible, but the student might at least try to beg for one of the color model or maybe the parent will care about the student not destroying his eyes on a non-backlighted screen. As for the CAS model, it's banned in standarized tests and stuff.