Yes, you can make heavier cuts. That said, you start to stress other parts (Like the X/Z gantry) so there is a limit to what is possible.
I got the spindle for a variety of reasons - one of the big ones was collet size availability. I purchase a fair number of bits that are in metric - so having metric collets was critical. I have a complete ER 20 collet set from 1mm up to 16mm. Just the ability to use 8mm, 10mm and 1/2" is reason alone.
Another factor was noise - my neighbour across the street was complaining about the noise when I worked into the evening. And with the Dewalt 611 I always wore hearing protection. Last night with my spindle, I was cutting Aluminium - and could have gone into the wee hours without anyone hearing. I don’t need hearing protection (for most cuts - sometimes a heavy cut in wood starts to be noisy. Loudest thing I have now is the shop vac - need to put that in a box and kill some noise!
Throw in the automatic on/off controls. And speed control, and range of RPMs.
Ease of tool probing. No motor fan blowing the dust everywhere (if you go water cooled).
Granted its a lot more than a Dewalt 611 - that is the only downside. But you won’t look back once you cross over!