The JX3P is a pro level board (although an old one) whereas a "cheap" Casio would be a consumer level - for that reason alone I would choose the Roland over a Casio. In addition, the Roland is a classic (maybe not as classic as
a Juno 60) but it should hold some value (certainly better than a Casio).
The MIDI application of the Roland will be limited (given it's age) and very possibly a Casio may have broader MIDI application - but the symth programming on the Roland would likely give you a better education than a Casio).
Keep in mind there are many different types of synthesis (Roland uses something different than Yamaha, than Casio, etc) so learning to program the Roland does not make you a whiz on all the other method. However, the method used on the JX3P is pretty easy to understand. The Roland does give you actual knobs to tweak - vs. scrolling thru windows) which is a more enjoyable way to program (at least in my view).
$170 Ameican may be getting close to the high end value for a JX3P (certainly no more than $200). However, there may be some vintage guys that may debate that. The stand and the pedal may add about $30 of value.
I will add that as you progress as a keyboard player you can always find a use for a JX3P - you likely would outgrow a cheap Casio very quickly,