I have done this before on a 1000cc bike, as I am sure a lot of you guys did. It was well worth the investment. The difference was night and day, especially because the whole package was not as quick steering as the KTM (but what is?).
The 790 has very quick steering bike to begin with. If I wanted to lighten the steering more, I would look into lighter and/or faster steering set of tires (have good experience with Dunlop Q's but not on the 790) and probably for other ways to lighten the rotating mass of front wheel assembly, such as lighter discs as suggested by my esteemed colleague, above. I like the Galfer products and had very good experience with them in the past (both discs and pads).
If I wanted to spend ~$3,000 on the bike (over 25% of its new value) I would put it in braking (going with the Galfer discs will probably serve both goals -- braking AND lighter steering -- well), suspension and maybe pipe and remapping. Would cost about the same as a set of lighter wheels. That said, I completely understand that different riders have different priorities when it comes to performance and looks.