I suspect this is very much a matter of personal preference, if you are comparing one shot colour CCDs with a cooled spectrum enhanced CCD;
the reason I went from a DSLR to a cooled CCD is simply noise
With a DSLR I had to take 6 to 7 dark frames-for 10 minute subs that's over an hour and when you go to 15 min subs-well that's a lot of time-and in fact people recommend you need to take as many darks as you take lights
my particular CCD is very low noise-many people don't even bother with a dark, I might take one or three depending on the night. This is virtually not possible with a uncooled DSLR
a cooled DSLR is probably on par with a cooled One Shot Colour CCD. Costs about the same too
there are pluses and minuses of course
the CCD is laptop dependent; rough framing can't be done by squinting through a view finder.
A mono CCD is much more sensitive of course but requires other accessories such as a filter wheel
when I bought my QHy8 I think it was actually cheaper to do that compared to buying the cooled modded DSLR.
course you could buy a used 350 D for 400$, take off the filter yourself and build your own peltier cooling using parts from a travel fridge-there are plans available on the internet.
noise profiles also vary depending on the model of the DSLR. My 300D was very noisy; the 350 D is much less; maybe newer models have progressed further in terms of noise reduction