Depends on what you mean by lightweight programming. If you are building anything in a compiled language that runs for over 10 minutes, I'd say you could like benefit from the extra RAM (either now or in the next couple years, once the laptop is dated). If your programming is simple data processing that runs in a handful of seconds, the extra RAM shouldn't matter. The X1 Carbon is a better difficult case to get in and the RAM is soldered on, so you can't upgrade it later. For that reason, if you anticipate your needs changing, it might be work it to upgrade the RAM now.
I do agree that an upgrade from HHD to SSD is the first choice upgrade for your money.