Skylake Upgrade Worth It?

My last build was April 2012, with last update in Nov 2013. I tend to skip at least one gen when it comes to CPU and GPU architecture.

I have 6 weeks holiday coming up in the next few months and I'd like a little project to do, followed by catching up on some of my older games and getting into at least one new one (Witcher 3).

Given my current architecture, is it worth upgrading to a new Skylake build, or should I just look at updating GFX?

I'm not too fussed about budget, but if I do a rebuild, it'll be a complete rebuild (except PSU/Sound/SSD/Monitor). Regarding the monitor, I would possibly look at updating that next year when a decent 120Hz IPS Freesync/Gsync becomes available at a reasonable price (maybe there is already, I haven't kept up in that regard).

Current Spec

i5 2500K 4.5Ghz 1.3v
Asus P8Z68 Pro Gen3
Corsair 16GB Vengeance DDR3
Corsair H80 Cooler
Crucial M500 480GB, Crucial 256GB M4, WD Caviar Green 3TB 64MB
AMD R9 290
Viewsonic VP2770
SoundBlaster Z
EVGA SuperNova G2 850
Windows 8.1 Pro 64bit

Don't chastise me for not filling in the 'new build' template, as I'm not speccing right this second, just asking if it's worth looking at.

I'm not seasoned by any mean of the word, so don't hold my word as gold. I'd say it depends on what you are looking for. In general terms your rig is still very relevant and capable. I had exactly the same board and cpu (still have them in a box, need to sell soon) and it had no issues playing iracing foe me on triples with SLI GTX 680s. I started to have issues when I added a fourth monitor and started streaming all on the same rig. That was the only reason I decided to upgrade to a 4790K and board, after contemplating 2600K for a while for the extra threads.
If you are not having any issues I wouldn't worry about it too much. If you are one of those that just has the itch to upgrade then go ahead. But to answer your question it's not worth it unless you are having issues.

I upgraded from a Phenom 2 to an i7 skylake. How much of a difference do I notice? A decent amount. Was it a $1600+ difference? (I didn't really use anything from my AMD rig other than a few HDDs) NO. I could have waited for Zen or what ever comes out after skylake but I had the money burning a hole in my pocket and I was tired of constantly tweaking my AMD rig.
I'd say keep what you have and get another 290 to xfire.

If the money isn't a big deal then why the hell not.

I was in the same position when I jumped from an i5 2500k to a i7 6700k. Here are my thoughts (you can see my sig to see how my old system stacked up).

The Sandy Bridge part is very capable and if your only objective at this time is increased gaming performance then the GPU is your best bet. However, if you have other CPU dependent tasks and/or want to enjoy the benefits of the Z170 chipset, then a new build is an easy choice to make.

I did see a noticeable improvement in gaming moving from SB to Skylake (I kept my GTX 780), mostly in minimum FPS and GTA 5 was a tremendous improvement. Overall, I felt that the upgrade was worth it, but I am keeping in mind that a new GPU in the Spring will really unlock the performance of my Skylake build.

The PC Perspective Discrete GPU article which compares SB to Skylake is a good read and should help you make your decision.
http://www.pcper.com/reviews/Graphics-Cards/Skylake-vs-Sandy-Bridge-Discrete-GPU-Showdown

When I went from my i5-2500k running 5ghz to the current i7-4790k I paired with a video card upgrade so my experience is probably very biased that there's a huge difference.

To be honest if you can sell the i5-2500 or give it away to someone it's worth it. But if not, probably would keep on to it for a few years.

Thanks for the input all , tho' I must say I'm still fairly undecided. I'm pretty sure I could sell on the CPU/mobo/RAM combo and the 290 as well, so that may well sway me over.

IF I go Skylake tho', should I look at 4 core or 6 core? 6 core would seem to suit gaming better as games seem to be using 4 cores more now and it'd leave 2 free for OS, but is the performance the same?