I have a fairly large OnQ Unity set up. I also have Control4 in my house and separate pool control system. I went through some of the same trades that you are and would be happy to share my experience if it still helps. I own a pretty large house. First time poster so apologies if I mess something up. I usually just read everybody else's great ideas and try to use them.
OnQ: I have 6 cameras (2 video intercom), 4 music zones, ~10 intercom stations, one LCD panel, 3 TV interfaces, ~50 light controls, etc.
The OnQ system works pretty good and has been pretty reliable. The biggest thing to remember is there is NO hot swapping of units. Make sure everything is powered off. After that it's pretty easy. The main reasons I went with OnQ was good bang for the buck and I could do the install myself.
LCD panel: I only have one and only need one. It is much easier to control the system through iPad, iPhone, or Macs (we're an Apple household). Control and configuration is all done through web browser instead of sexy app like control4. I like it better. I can view the cameras on TV's or any browser window, easy peasy. There are very few things that you can only do through the LCD, like updating software.
Music zones: Do you really want them in every room? My house has lots of common area. I have a zone in the basement, kitchen, upstairs/entry, and on the deck. We use them mainly as background music. I have one local input for iTunes, but setting up the music player isn't too hard. Won't work with newer mac OS's though. We use internet radio most of the time. I may add a zone to the master bath someday but really don't want them in all the other rooms. Kids all have bluetooth speakers anyway. I'm not an audiophile and not trying to pump a party's worth of music through them.
Intercoms: Work great. Big house so we use them a lot to yell at(for) kids
Automation: I get it that some people don't think this is good for that. However, my outside lights come on just before dusk and go off at dawn, adjusted daily via internet weather. I have lots of lighting scenarios and they work great. My wife likes that we can turn every light on in the middle of the night with just one iPad selection. I play recordings out my kid's intercoms on b-days, stuff like that.
Lighting: I actually bought this first and then added on all the other stuff. Pretty happy with. If you don't have deep switch boxes though, you'll probably be replacing those too. The switches take a lot of volume.
TVDI: Works OK. I think it's a pain to have to manually switch tv inputs and use yet another remote but that's the way it works.
I want to add some other things eventually like video recording but just haven't got to it yet.
I used Control4 in my home theater. I wanted good video selection. The level of programmability is great but it really irks me that I can't expand the system myself and it is so expensive. I hate having to call someone out to do something simple. There is s/w available to homeowners now that gives them more control over what's there but not worth my time to learn. It's great in the home theater but not for me anywhere else. It's a relative system too, so if the kids come in and press a lot of component controls it gets confused. Hang on to the old remotes, you'll still need them. The mobile interface is great but I use their small remote more.
Pool Control: They all suck.
Hope this helps you out.