When I got around to watching Dave's teardown on the DS1054Z i was very surprised to see that it only had an 8 bit AtoD.
Yes, it has an 8bit ADC, like some 99% of today's digital scopes. There are very few scopes out there with a hardware resolution of more than 8bit (like the LeCroy HDO Series with 12bit ADCs, the Keysight DSO-S with 10bit, or some PicoScopes with I think up to 16bit, and the OWON XDS with 12bit ADC).
Some scopes have a HiRes/ERES mode to get to more than 8bit resolution through oversampling but that comes with various drawbacks, like a reduction in bandwidth.
The HMCAD1511 is impressive on 1 channel at 1GS/sec but you have to divide by 4 for all channels. What little bit of signal processing I can remember (from long ago), you really want >10 bits of resolution and >10x sampling rate. This makes a DS1054Z a bit "sketchy" when in 4 channel mode !
No, it doesn't. For the majority of scope applications, 8bit is just fine.
As to sample rate, as long as it satisfies Nyquist-Shannon (f
s>2*f
0) you're fine. In 4ch mode the DS1054z samples at 250MSa/s, which is enough for signals up to at least 100MHz. As long as the sample rate satisfies Nyquist-Shannon for your scope's analog bandwidth then that's fine, and a higher sample rate than that becomes pointless.
Now, for signal processing you very much want more dynamic range than a 8bit scope offers, and then you'd either opt for a scope with a higher resolution ADC (i.e. Keysight DSO-S or LeCroy HDO) or better, a proper Signal Analyzer with 14bit or 16bit ADC instead of a digital scope (which is a Waveform Analyzer).
For the price, is is still very impressive, but there is a huge jump in $$$ to get to the DS2000 with higher resolution and (I believe) higher sample rate.
Higher sample rate, yes. But like the majority of digital scopes the DS2000 is still an 8bit scope.
Is there "room in the middle" or can the DS4000 be re-engineered to down to about the price point if the DS2000 ?
What for? The DS4000 is just a 4ch variant of the DS2000, and again 'just' an 8bit scope.
Or am I making a mountain out of a mole hile ?
You are, actually. A short look at the specifications of the DS2000, DS4000 and a few other scopes would have shown you that 8bit resolution is, in fact, the standard for a digital scope today.
Also, you haven't said what your actual measurement problem is, which very much decides which instrument will be most useful. If you want to do signal analysis then you can still do that with an 8bit scope if you can live with the lower dynamic range, if not then I hope you have deep pockets