If you are able to practice mostly at loud acoutic piano volume and only once in a while need to be quiet, go with the acoustic with mute pedal. Acoustic is still better than any DP. If you need to practice mostly with the mute pedal, forget it. Get the NU1. The mute pedal is an inadequate solution for anything other than the occasional. With the mute pedal, the resonance of the acoustic piano is mostly muted, which is a major benefit of having a real acoustic over the NU1 to begin with. Also, the mute pedal alters the feel of the action, and if used all the time, you could develop the habit of pounding on the keyboard harder than you otherwise would without it. If I had to practice on my upright with its mute pedal more than 50% of the time, I would replace it with the NU1. It's a no brainer.
Another alternative is to get an acoustic upright anyway but ask your tech to replace the felt with something a lot thinner. That way, it doesn't mute the piano all that much, perhaps just enough to not get in trouble with the neighbors. The felt would wear out much faster, but it's better than the standard ones Kawai provides, which mutes the piano far too much but last a long time. In any case, you should use the mute pedal knowing exactly how your playing should sound without it, meaning, you need to have practiced a lot without the mute pedal. Otherwise, if you practice to sound correctly with the mute pedal, your playing will sound all messed up without it. The mute pedal is particularly handy if I need to practice a forte passage of say 6 to 8 measures for 30 minutes to an hour straight. Without the mute pedal, I either go deaf or my family wants to hurt me.
