I'm with you on this. Tried a couple of modern hardtails and found that while they are flattering in some situations (very steep rough chutes) they are much less engaging when not riding as fast as I could at 10/10ths of my ability.
I did find they encouraged me to ride more difficult trails that I'd normally bottle, which was great. Funny thing is after riding them a few times on the modern bike, I was able to go back on my 2010 XC hardtail and get down them all right, albeit not quite as confidently.
I'd say if you're able to confidently ride all the terrain you want to be able to ride on your current bike (it's that awesome zaskar, right?) there's not much advantage in swapping.
If you want to progress your riding (bigger, steeper, rougher etc) beyond what you're currently comfortable with, a modern mtb will almost certainly help.
Personally I'd be looking for something with a slacker head angle, nice modern components, but not too long reach, as it's the latter trend for long bikes that seems to suck some of the fun out for me.
All the above goes double for 29" wheels IMO.