I'm in a similar situation, except instead of Chemical Engineering it would be Mechanical Engineering / Engineering Management / MBA (still deciding =P) and that my company pays 100%, up to a maximum of $10,000/semester, which works out to roughly a maximum of 2-3 classes/semester.
I agree with brewer12345. I'm still a little pensive because I could see a lot of other stuff going on realistically soon next couple of years (buying a house, getting engaged and all the stuff that goes along with that) and things in the not-so-distant-yet-not-so-near future (kids).
Not to take over the thread but, my main concerns are not having enough 'time / motivation / mental fortitude' after a draining full time job to complete masters-level engineering coursework (MBA might be easier) or have too much other stuff going on.
However, if I don't get my masters in the next few years, once I have young children I think it would be out of the question, since while I'm working my way to FI, any free time I see myself wanting to spend with them, not studying or doing assignments.
Ultimately in your case I wouldn't sweat the 25% cost. Think about the intangibles that you place value on and have that help you decide whether it's worth it.