If you have the extra money then upgrade but if it was me I would keep your cpu/M.B. since you are not going to get a huge upgrade inless you are going for x99/x79. I would spend the money on waterblocks for the vid. cards and a water block for the M.B.,maybe some more ram even though you have 16gb you could fill up your 2 other slots,sleeved cables for the psu and the do the other things you mentioned in your post.

 The only reason to upgrade from what you have is if there is a feature you can not achieve with your current system. M.2? I can't think of any.

I am on 46 GHz on my ASUS Maximus V Extreme Z77 and had it running the same on my ASUS Maximus V Formula Z77.
My Maximus V Extreme Z77 holds my 5 GHz Record.
I would say No it would not be worth it. By the way Nice Looking Rig.
I would have given you a +1 if you had a  setup.

Don't know why ya would buy a new board plus CPU just for aesthetics. Just pull the VRM block so it simplifies the loop and quits restricting the flow rate, and depending on how much air flow the case has add a fan to blow across the VRM area if it needs it.

Better keep Z77 until X99 show up. You can prepare watercooling parts if you want.
GPU blocks, new tubes, radiator, reservoir and replace and for 2-3-4 months if you like X99 performance.
i7-4790K is better CPU than 4770K, 500MHz faster and best option if someone no system or have old system.
But with X99 you will get and visual and performance, more cores, newer memory standard, DDR4 Quad Channel.

I don't know I somehow think that upgrade on at least i7-5820K is better if someone need new rig now, special if we talk about someone who is not in financial situation to change mind for 6 months and cross on X99.
New memory standard is here and don't even to talk about long term of DDR4 upgrade and Intel 6 cores. Now start new race by memory manufacturer immediately when first people build rig, they will start to offer faster and cheaper kits only to pull more people to upgrade on X99.
But we still didn't see performance of that processor, temps and how well OC that's most important thing in hole story.
If motherboard support SATA Express or M.2 closest feature what I can see as something new is PCIE 4.0 gen on Skylake. 
That's for two years and how much will be improvement will be visible. For 4790K paying similar price for everything  and look all others who upgrade on DDR4 and you just build new DDR3 platform... I don't know... i7-3770K on 4-4.5GHz is very close to new Haswell processors... I mean we talk about upgrade for 10-12% visible only in test for processors, with same number of cores and several years old DDR3 in time when fast 
DDR4 is available and 6 cores Intel.
 

For me is enough 28 with i7-5820K for strong single card. 
My ideal system would be i7-5930K on 4.0GHz with EVGA Classified graphic card fabric overclocked as now. 
But with i7-5820K I'm satisfied too, special if work stable on 4.0GHz(700MHz+) because I don't think on SLI. 
Next will be same class submarine.