Is this Klipsch upgrade worth it?

How big the room?

From what I read people like the Forte very much,  I don't think it would be a big upgrade. LaScala would take you up a giant step.

Fwiw, I demoed the Forte III when that was the current model and was surprised at being underwhelmed. As a Klipsch fan, I had original Heresy and KG 4.2 for years, I then demoed the Heresy IV and thought it superior to the Forte. I was looking for a bigger sound though and tried the Cornwall IV's. I bought them and 1.5 years later I'm still very happy.

I also demoed a range of solid state integrated amps with the Cornwall IV's in the 10k price neighborhood. They all sounded excellent. In the end I bought a Luxman L509X that I liked best. Always loved the clean look and pure, uncolored sound of Japanese gear.

Mofojo, my room is 16x16, with around a 12ft hole opening into the kitchen.

No I would not make that upgrade. I have heard both and the current La Scala (at two different dealers). The Cornwall iv and La Scala were in the same room with the same front end at both dealers.

The Cornwall IV has the potential to have harder hitting bass depending on the room. Get it just right (kind of close to the front wall) it hits harder. The Cornwall is a little softer in the bass on the leading edge but easier to place on the room and far less room dependent. If the bass is good with your fortes I would look at upgrading something else or saving and going for broke later lol. The mids seemed to spread out a little more on the Cornwall. Hard to say as they were in different rooms (heard them back to back though). 

The La Scala is a different animal and could be a worse speaker without subs. They have NO bass extension and need subs. I heard them without subs and they sounded really thin and dry to me. I felt like I could hear the wood but that could be in my head. Sounds different than MDF. They have a very strong horn sound, Wide soundstage that maintains focus. Listen before you buy for sure. With the latest price hike they are getting up there.