If it's bandwidth and memory you want and you're not uncomfortable (for practial or other reasons) to "hack" the scope I think the DS4000 STILL brings a lot of bang for the back. You get a 4GSs/s scope with a bandwidth well above 500MHz, 140Mpts of memory and all the decoders and triggers. But yes, it's at least 6 years old so certainly not new and will soon be superceeded by the new models but my guess is that those models will A) be (or try to be) more high end and therefor more expensive than current models and B) not easily hackable.
There will always be something new "coming soon" and once it's out it's just that - new - likely having some issues that may or may not impact your specific use case so you wait around to see what issues boils to the surface and what fixes are provided by the manufacturer and once the product is "mature" you start to think about if it's really worth getting "this old model" when there's likely a new one around the corner....
So really, the benefits of the RTB2024 would be the better user interface.
Don't forget the 10bit ADC and the fast web-UI (if that's useful to you).
I have a DS4000 and as a hobby user I'm generally happy with it considering it was - by far - the best deal I could get back in 2012 and at the time there wasn't even a hack for it. It's died on me once but luckily I was able to repair it. I would've replaced it with RTB2k had I been allowed in on the introductory deal but unfortunately R&S reserved that for a specific part of the world and at list price, without a hack it's just too expensive -
for me - YMMV of course.